The following are tips I've learned from traveling to Sierra Leone for the past 20 years.
Medical - In order to obtain a Visa, you must have a yellow fever vaccination. In order to survive Sierra Leone, you will need many more. Work with a doctor that is a travel specialist. Universities are your best bet. Start two or three months early. Once you are in country, you are really your own doctor. I carry a small first aid kit, but also I do not hesitate to ask local people if I have a small issue (ie: minor infection). Dehydration and small infections are your biggest challenge.
Evacuation Insurance - travel insurance is a good idea. Plans change, and things happen. I usually pay about $50 for this insurance, but have never had to test it!
Visas - Click here for a link to the Sierra Leone Embassy. Again, you need to have you shots prior to applying for the visa.
Flights to Sierra Leone - You get to Sierra Leone by way of Heathrow International, London. There are three flights each week with BMI Airlines. Flights are arranged through McPhillips Travel Agency in Baltimore, Maryland 410-659-7776. They are very, very helpful. BMI flights are a no-frills airline, but they get you there safely. Historically, when you arrive at Heathrow, you have to retrieve your bags and go through customs. You then check back in for your flight to Sierra Leone. Because of this, you need three to five hours at a minimum in Heathrow. Just recently there is a "check through" service where you can check your bags and skip this extra step. The biggest key is the weight for your bags. Keep them under 50 lbs., really! Weigh them. You will be charged for anything over weight. You will see people all over the BMI waiting area pulling things from their bags because the bags are over weight.
Flights from Sierra Leone - BMI is also your flight out. When in Sierra Leone you need to contact the travel agency in Freetown to confirm your spot on the flight about three days prior to departure. The phone number is listed on your ticket. You can simply call them via cell phone and make this confirmation. You arrive at the airport many hours ahead, wait in line for a long time (having water is a key), and then make your way through inspections, check in, more inspections, and then finally wait in a lounge for hours until the flight. This is a long process, but relax.
Cell Phones - Everyone has a cell phone in Sierra Leone. You only pay for calls you make, and pay nothing for incoming calls. You can "top up" a phone anywhere by simply buying a card and inputing the code into the phone. I never have a phone. When I need to make a call, I buy a card for much more than I need, make the call, and let the person enjoy the extra minutes I put on their phone.
Clothes - I dress in shorts (with big cargo pockets), a t-shirt and rugged sandels almost the entire time. Three shorts total, four t-shirts, a few pair of socks, one pair of tennis shoes and a decent hat is about all you will need. A pair of sunglasses with a neck cord is very helpful. One bathing suit can substitute for a pair of shorts. Anything else you can get there. If you have more than a backpack, you are way over packed. You can have nice shirts made anywhere in country. You can get help doing laundry anywhere as well. During dry season (Nov - April) things dry very fast. In rainy season (May - October) nothing dries. For women, if you are up country, you will want to cover your thighs to be respectful to the culture. You can easily get a lapa (one piece of cloth). The women will be thrilled to help you pick one out, and teach you how to tie it properly.
Shoes - One cheap pair of flip flops for bathing and hanging out. One pair of decent sandals (that protect your toes) for walking around. One pair of tennis shoes for long walks.
Luggage - Travel light. A good backpack is very important. Don't pack giant duffle bags with tons of stuff to give away. Not necessary. One decent duffle bag to pack items you purchase (baskets, gifts, etc.) is nice to have for on the way home. Bring an open mind, respect and curiosity. Leave with a lifetime of memories. If there is something you really love (meaning a physical object) leave it at home.
Laptops - The best laptop that can take the weather, the dirt, and the travel is called A PAD OF PAPER. If you must bring a laptop, realize it might not make it back in one piece. Backing up your data on a portable mini drive is a good idea. See "Power" below for more challenges.
Power - Electricity is available in Freetown, sometimes. Electricity is available up country, never. I make sure everything I use that requires power will run on AA batteries. I buy one giant stack at Costco. When they no longer have enough power, give them away. They will still have enough life for small lights or other creative uses. I'm going to experiment with a solar charger, so stay tuned for a report on how this works.
Internet - Now available all over Freetown, Makeni, Bo and other places up country. The connection speed is slow, but you can read email and send responses easily once you reach these locations. Enjoy "getting off the grid" if you can. One cool trick is to scan all key documents and email them to yourself. If you find you have lost something and you need a copy, you simply go to an internet cafe, open your email and pay a small fee to print. Remember to delete all temporary files because otherwise your document is still on that computer.
Lungi Airport to Freetown - Once you actually arrive in Sierra Leone, you still are not in Freetown. You are at Lungi International, which is on a penninsula located across the Sierra Leone river. You have to make your way from the airport to one of three choices. First choice is to take a helicopter ride to the Aberdeen area of Freetown. This is expensive, kind of "exclusive," and slightly dangerous. A second choice is the hovercraft. You take a transport from the airport to the hovercraft facility, wait in line, and then take the hovercraft again to the Aberdeen area of Freetown. This costs a bunch of money, again is exclusive, and does not always run. The third choice is the ferry. You have to take a taxi to the ferry (about 15 minutes), wait in line to pay for the ferry ride, wait in line to load the ferry, and then enjoy a relaxing ride across the Sierra Leone river with many friendly people. Once you get on the other side, you either head straight up country, or work your way across through the crowded Kissy section of Freetown. It all depends on where you are going.
After all the years of travel to Sierra Leone, this is what I do... I stay the night near the airport, enjoying a calm meal and nice visit with friends. No rush. No hurry. No need to "catch the ferry." The next morning, I take a taxi and get to the ferry for a relaxing ride on a very empty ferry (no flights and passengers at this time of day). I meet the CIP team on the other side, and head straight up country.
Getting up country - You have two options. The first is public transportation. It's not as reliable or fast, but it's very, very inexpensive. Ask others what the cost is BEFORE asking the driver or his apprentice. Know your prices, or you will get an inflated price. This is a super option if you have the time, and want to get to know the people. The second option is to arrange for private transportation. If you do this, you are responsible for fuel, the driver, possibly the apprentice, oil, tires, etc. This can be expensive, but it is "oh so" convenient. When I travel up country with a driver (and the team), I cover their costs for food, etc. and provide a small per diem. When they go "up country," they are traveling. We go as a team, and act as one. Drivers love to drive fast; feel free to request a slower pace if it makes you nervous. Stop every chance you get. Rivers are amazing. Roadside stands offer incredible food options. Just stop to experience. Locals are used to what they are seeing, so they may be more inclined to "get there."
Money/Banking - You can buy anything you want or need in Sierra Leone, if you have money. The best currency to carry are US dollars (in $100 increments). Smaller bills (ex: $20) are not useful. You can change them almost anywhere, and there are banks located in Freetown and upcountry. The less money you have, the more you will be able to understand how people live. If you are traveling with CIP, discuss security of your documents and your funds with the director. If you are on your own, be smart. A credit card MAY be used in a bank, but no where else in country. They are useful while traveling through Europe, but not of much value in Sierra Leone. I hear ATMs are coming, but don't make it part of your plan.
Weather - In dry season (Nov - April) it's hot and dry. In rainy season (May - Oct) it's hot and wet. The clothes are the same for either time. During the dry season, the roads are dusty, making it hard to travel sometimes due to the visibility. During the rainy season, the roads are full of potholes and standing water, making it hard to travel sometimes. Hey, it's Sierra Leone!
Water - You drink lots of water here. You can buy bottled water all over country, but it becomes expensive and a pain to haul around. I have recently started using a steripen, which zaps the water with UV rays and makes it safe to drink (so they say). I carry it on my belt, drink water anywhere, and just replace the batteries once in awhile. It was great. I also drink rain water during the rainy season, and know of a wonderful spring near Makali.
Food - If you are interested in cooking American or European foods while in Sierra Leone, stay home. I'm not kidding. Go and learn how foods are made (participate in the process). Ask about cultural norms, and follow them. Learn how to eat with your hands. I eat rice, cassava, potatoes, yams, fish sauce, roasted goat, monkey (rarely), all kinds of fruit, fish and anything else that is available. When I eat, I share with everyone around me. I drink the palm wine, but find it disrespectful to drink beer (very expensive). I may buy a canned soda, but then take a sip and share it with everyone around me. When I stay with others, I make sure they are reimbursed for any additional costs they incur to help feed me. When you visit a community, they know you are a visitor, and often greet you with food. Enjoy.
Language - Sierra Leoneans speak English (learned in school), Krio (used as a merchant language) and native languages (such as Themne and Mende). Krio can be learned in days, but not mastered in a lifetime. Try Themne or Mende too, showing respect just for attempting the language.
Photography - I take lots of pictures, but I am with people I have known for a long time. I take the pictures, print them when back in the US, and then bring the pictures back on my next visit. I always encourage family portraits because it is a great opportunity for a family. When you are in a more public place (like a market), be very respectful and only take pictures if someone says it's ok. Sit down with someone. Talk with them. Learn their name. Tell them who you are and why you are there. How would you like strangers to take your picture if you don't even know them?
Mosquitos - Sleep without a net and you'll get lots of bites. Get bites and you will scratch. Scratch and you will open a sore. Get a sore and it will get infected. Lotions with deet work.
Lodging - If you stay in Freetown, there are tons of options with prices ranging from $5 to $150 per night. Up country I stay with families, participating as a member and giving the host a small amount of money to offset their costs. When I travel with CIP, I give them an idea of where I want to go and they make the arrangements. If you need four star accomodations, go to Europe and just read adventure books about Africa. I prefer beds with native matresses, a decent mosquito net, sharing a latrine with many others (one at a time) and living life as they do.
Bathing - In Freetown, you will probably have access to a shower with cold water. Up country, you get a bucket of cold water, probably drawn from a well if you are so lucky. Your host may offer to heat the water for you, but understand that this requires someone to go a long distance or spend money for firewood, and then spend a lot of time heating it for you. Go to the well with your empty bucket, fill the bucket, carry it to a baffa (bathing area surrounded by palm fronds), and pour water over your head. I've washed at midnight during a tropical downpour, standing in a swamp and under a bright moon. Again, it's Sierra Leone.
Freetown v. Up Country v. Village Life - Freetown is a country all to itself. There are big buildings, stores, crowded markets, beautiful beaches, rich people and anything you want if you have the money. Up country is a different world, with towns and markets and a pace of life that you have to learn to appreciate. Village Life is like traveling back in time, with villages surrounded by food, and time to actually learn to know everyone around you. These worlds don't mix very often, with villagers rarely traveling to Freetown etc. It's all Sierra Leone.
Compensation, Team - When I travel with the CIP Team (Manfred, Patricia, a driver) I take the opportunity and show my appreciation. First, I make sure they have money in their pocket just like I do. Manfred can be a helpful guide as to what is appropriate. Second, at the end of the adventure, before heading back to Freetown, I give them each money. Why upcountry? They use the money to buy food for their families. Up country, the money goes a long ways, with four times the spending power compared to food in Freetown. Also, we have a vehicle so they can transport this food back to Freetown conveniently. I do this because they are my friends. I live comfortably in the United States, and they live below the poverty line under difficult circumstances. Maybe I do it to make myself feel less guilty for how I live back home. 
Compensation, Village Hosts - As I stated under "Lodging," I compensate anyone who hosts me upcountry. I do this through Manfred (the director of CIP), showing respect and acknowledging the cultural norms. All transfers of funds are done in private.
Toilets - In Freetown you will find porceline toilets that may be flushed with buckets of water. As you go up country, you will find latrines of various types, but the concept is all the same. It's a hole in the ground. Prior to going into the latrine, ask for water. It may be in a bucket, or in a plastic "teapot." You take off your pants, squat over the hole, and take careful aim. Pour the water with your right hand to clean yourself, and scrub with your left hand. Toilet paper is expensive, and not worth the effort. Prices - It is very useful to know the current prices of common items in Sierra Leone. By paying market price, it helps to prevent tourist inflation. Check out this site for current prices.
Feminine Products - You can get these items in any town upcountry or in Freetown. No worries.
