Just read the pinned topic on cycling your tank BEFORE adding fish (this can take 1 to 2 months). Also BEFORE adding fish, look at what you want and then ask about adding them to your setup FIRST.
^^^ doing that lot will get you out of soooooo many holes!
Also consider:
Q) What size tank / fish are you thinking of getting?
Q) How much time do you think you'll be spending on it?
Q) How much money do you think things will cost?
Q) Are you thinking of having live plants as well?
GL
Andy