A major factor is "how much do you want to spend?" Carbon Fiber tripods are very lightweight but costly, Others may seem heavy to you but not to someone else. If you are using it outdoors you should get one without supports between the legs, that way you can swing out each leg independent of the others for uneven terrain and it may also go lower to the ground when needed.You also need to consider that some do not come with a head, you must purchase it separately while others come with either a Pan or Ball head. Make sure that it has a Quick Release Plate. You secure the plate to the bottom of your camera and then you just have to snap it onto the tripod head instead of screwing the camera on each time.
Also make sure that it can support the weight of your camera and lens. I would stay away from the lightweight, inexpensive "travel" tripods