Produce is often of very high quality. Meat and milk can prove difficult for western taste and diets, so be sure that all meat is cooked through. At hotels, you won't have any trouble, but if you venture into small villages, make sure that all water is filtered or boiled before drinking and all fruits and vegetables are peeled before eating.
If there is anything that can be called Tanzania's national dish, then Ugali would most likely win out. A polenta-style dish made with corn flour, it accompanies cooked meat and a variety of stews, and it's eaten with your hands. Recipes vary from village to village, and everyone has their own way of making it. Many foreigners find it bland and unappealing, but it's worth a try, and some upscale establishments serve it.
Tanzania's large South Asian community ensures that a great variety of restaurants offer cuisine from all parts of that region of the globe. All eateries near Hindu temples particularly in Dar are a good bet. Just watch where the local Indians go to eat, and you won't be disappointed. Most of the food is cooked in large amounts of Ghee, clarified butter, which can be hard for some people to digest.
Msumbi Coffee Shop
Northern Tanzania has a number of great coffee plantations. Although coffee does not have the same popularity in Tanzania as it has in Ethiopia, with a bit of searching you can find a decent cup of java, instead of the instant "Africa" coffee that is served in most restaurants. All large hotels in Dar make good coffee. If you want to brew your own cup, Msumbi Coffee Shop, +255 22 260 0380, Sea Cliff Village, sells Tanzanian coffee beans ground or whole, roasted on the premises.