All of what Justin said... plus:
1) Understand the lighting requirements of your specimens - not all coral are created equal. I have many SPS on the bottom, while some of my shrooms/LPS I place high. There is no one size fits all and understanding this could save you lots of coral and get better health/growth in the long term
2) Feed that reef! Corals eat - thats what those polyps are for. Although they get energy from photosynthesis with the zooanthelae in their tissues, they will readily eat when happy. Interestingly I find fish poop seems to be delicacy for many SPS - LPS typically will love a more meatier treat.
3) Watch the deltas - in all params (temp, ph, alk, Ca, Mg, etc.) When things get out of balance do not overreact and correct immediately. Keeping them stable is ideal, but inevitably a correction will need to occur - just realize that doing it right away could cause more problems then it solves.
4)Look into mechanical filtration media (filter socks, etc.) and change them often. In my mixed reefs I add a bit of food and you will want the extras out ASAP - those socks work wonders IMO. Regular water changes also work wonderfully in keeping certain params within bounds (esp. Nitrates)
5)When placing corals, realize what gets along with what and try to accommodate. Its inevitable those damn hermits/snails/current/etc. WILL blast a coral into another. Knowing what needs a wide berth vs what 'could' touch for a little while could mean the difference from immediate death vs a small bleached spot that can be recovered from.
Lots more...but I think this is some of the main ideas that come to mind.