My experience in Tanzania was fantastic. However, when it comes to packing and getting my act together I can often be a bit rash. There were many things I did not bring which I wish I had; there is such a thing as under packing! A flashlight is a must, since power outages occur often. I would suggest bringing at least two skirts, I didn’t bring any and had to buy one in Zanzibar at muzungu price (made in Thailand!). I would also suggest bringing a side project or lots of books. We had a lot of free time and another project would have been useful, especially if your internship involves a lot of waiting. A small first aid kit including pain killers, medication for nausea, bandaids, etc is also useful. All this being said, be careful not to over pack. It is convenient if you will be moving around a lot to fit everything into a back pack you can easily carry, that way you can walk to hostels if taxis are charging too much (they will often follow you and lower their price when they see you walking away). Also, the phone providers in Tanzania have Internet packages which are inexpensive and useful when Internet is hard to find. I would suggest bringing an unlocked phone that you can access the Internet with, that way you can easily send emails home.
Travelling in Tanzania can be a bit stressful, but most people are friendly. And if you ask, most people will give you directions, just be careful of touts. You can obtain information about travelling to the next city and how to get around from the staff at your hotel. Be careful when buying bus tickets, try to get a Tanzanian to buy them for you, or find out the real price before going to buy them. Always buy your ticket a day or two before your trip in order to avoid hassle the day of. Also, be aware that buses might not always be on time and often are not in the best of shape. Try to be flexible and relaxed when travelling and stay smart. If you plan on doing a Safari it is easier to book in advance over the Internet. However, if you’re looking to save a bit of money and are flexible with your schedule, I would suggest finding a company you like before leaving for Tanzania and booking in person, usually out of Arusha. If you go this route, be aware of prices and schedules beforehand!
Overall, I found Tanzania to be a safe and friendly country. Be sure to talk to people and enjoy your time!