when purchasing fish, always ask if it's reef safe, don't buy on impulse no matter how cute it looks.
here is a small list of reef safe fish.
most blennies are safe, all clownfish are safe,depending on the size of your tank, tangs are safe. anthias are safe, cardinals are safe, damsels and dottybacks are safe, but becareful, they are aggresive fish, gobies are reef safe, rabbifish are safe, they are two types of wrasses, reef safe and non reef safe, be-careful which you choose.
inverts:
hermit crabs, some becareful which shrimp you buy, some have special needs, snails are good, but some are large and can knock things over.
brittle starfish are reef safe and a good part of the cleanup crew.
choose your substrate wisely as some fish require it to burrow in.