First rule -
QT everything!
Rule 2 - never use tap water. Use
RO or
RO/DI.
Rule 3 - research everything before you add it to your tank. Your
LFS may be great but don't count on them, do your own research.
Rule 4 - put the more peaceful and less territorial fish in first!
Rule 5 - don't buy cute little fish that will outgrow for your tank. See rules 3.
Rule 6 - have a stocking plan for fish and corals.
Rule 7 - plan your aquascape so there are places for all the corals you want.
Rule 8 - space corals to avoid sweepers and (as much as possible) allopathy.
Rule 9 - run carbon to help mitigate effects of allopathy