Here are some general rules for buying a tripod.
1. The legs need to be long enough to bring the camera up to eye level with out extending the center column with the head attached. Extending the column makes the setup less stable.
2. The head needs to be a decent quality head. There are many makers of good heads out there depending on your price range.
3. The legs and the head need to have a maximum load rating of at least twice the weight of the heaviest gear you ever plan to put on it. This also helps provide the stability you need and want in a tripod.
4. The material the tripod is made of needs to be chosen with a few things in mind.
a. Whether you will be carrying it long distances or not. Carbon fiber is lighter and more expensive than aluminum.
b. What conditions you will be using it in. For general use or studio use Aluminum works just fine. In harsher conditions Carbon fiber is a better choice since the carbon fiber will not corrode as aluminum will if it is immersed in salt water or water with a lot of minerals. (depending on the minerals) If constantly in very wet conditions a good hard wood tripod is the best. Most people do not use them much as they are heavy, and expensive but they are the most stable choice in a tripod and work well in very damp climates.
5. Pick one with leg locks and control locks that you like and feel comfortable with. Manfrotto lever locks are convenient, however Gitzo's no twist legs are very rapid to set up with their twist locks. Gitzo twist locks are very reliable.
6. Pick a price range you can live with. Good tripods will cost a bit of money, but a good tripod, taken care of can last a lifetime.