Do you have a clean up crew yet? Feather dusters are nice as are 6line wrass, lawn mower blenny, Most angelfish are nice too. Damsels tend to get aggressive so you will need to make sure you are adding something bigger than they are.
You didn't say anything about your lighting or amount of live rock. If you are thinking about adding corals, you will need a protien skimmer and good lighting. Providing you have those, mushrooms are a good beginner coral. Button polyps are nice as are star polyps. I hope this has helped.
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