Read a lot of books, and listen to the experts!
Niger Trigger - 6"
Snowflake Eel - 8"
 Cleaner Shrimp - 2"
Coral Banded Shrimp - 2"
Tiger-Striped Star - 6" diameter
Sand-Sifting Star - 4" diameter
Various hermits and snails - 0.75-2"
Life's an ocean, dive it.
I'm 14 years old and love the saltwater hobby! Not much of a freshwater person, but I do breed Orange Sunshine Guppies.
Keeping anemones in a reef tank can be a challenge if you are not fully prepared.
Cultivating a nano tank can be an exciting challenge but unless you choose the right fish for your tank, you may be in trouble.
When you see signs of stress in your fish, you can then take steps to identify the source of that stress and then to resolve it before it becomes a major issue.