Do a lot of research, and make sure the one you get is one that has everything you need. No need to buy a tablet which costs more for features you don't think you'll need.
Also, don't think that because you have a tablet, it will make your art better. If anything, it will take a lot of getting used to, and will most likely be difficult for the first couple of weeks you're using it. It's just something you need to ease your way into, so don't be frustrated if your first couple pieces come out looking like shit.