Before buying anything like lights, substrate etc., you need to decide, more than anything else, how deeply involved you want to get and how much time you want to invest in your tank.
For instance, you may only want a low maintenance tank that requires only a minimum of work and looks nice. The more light you decide on, the more demanding of your time it will be.
Think about that and then respond with the size of the tank, the type of filtration you've got, the lighting you now have, if any, and how much time you want to devote to it.
Len