Emerald crabs, peppermint or cleaner shrimp, blue-leg hermits ... all reef safe inverts, with good lifespans in tanks.
I would avoid other shrimp + crabs, unless you know about them.
[Calfo + Fenner's reef invertebrates book is a good reference].
I would generally avoid starfish, unless you've read on them and have a proven stable system ... even so, only a few IMO regularly have long lifespans in aquaria [serpent/brittles IMO].
Best is to research before buying ... if that means coming home from the LFS after finding them [before buying] + checking online, buying a book + keeping it in your car ... but IMO there's so much variety among each type of creature, and given many don't do well long-term in aquaria or have competing needs ... worth investigating.
No simple answer, but if you ask about specific creatures - probably better answers.