I always opt for live rock and live sand. About 10 lbs of rock per gallon creates a good bio base. And always buy your clownfish in already bonded pairs. It makes things way easier, and they enjoy another clowns company (plus, if they really get along, they will breed and its really an interesting process to watch!)! Research what type of clowns you want, there are many types all with different personalities! If you want, an anemone makes a nice home, although it is not crucial or necessary. Different clowns prefer different types of anemones, so again, do your research. Depending on how big the tank is, I really only recommend one pair of clowns. They can get territorial. Try to keep the other fish peaceful, clowns will fight back if picked on, even when they are clearly outmatched (especially when protecting eggs).
I hope this helps with your tank C:!