better to wait a while. one of the biggest considerations is just getting down your maintenance routine so that everything is stable. i know the first 6 - 8 months i made a lot of bone-headed mistakes with my tank that things like clams and more sensitive corals wouldn't have tolerated very well.
you also want to make sure your lighting is up to snuff.
you will also have to decide which species you want to get. some are easier than others to keep. well maybe easier is a bit of a mis-statement. let's say somewhat differing in requirements, which may make them easier or harder, depending on your setup.