IMO- Well you might want to start with some T5 HO lighting depending on what you want to put in there... I have FOWLR (fish only with live rock) and that lighting is great. Next a nice fine substrate is probably best. Don't forget a bucket of salt, I use Instant Ocean. Hydrometer to test salinity, a salt water test kit, and some power heads (enough to generate 30 to 50 times the amount of flow per tank size). I use a power
filter to run media depending on water parameters. You may/may not need a protein skimmer down the road depending on your bioload. I would plan on it just in case. Oh another thing you will need is PATIENCE and TIME...
And this forum will be able to help out a lot... What are your plans for the tank? What do you already have? details are key...