If you know your size (75) which is a good size ( i wish I would have done that) then you should already start planning on paper what you need to set up. That way your cycle (where bacteria is created and amonia and nitrites usually spike), will not seem so long. Start looking on good deals on a

Tank
Stand (unless your a handy man and can make one).
Sump/Refuium
Skimmer
Live rock around 60 to 75 lbs (everyone has their opinion on this).
Plumbing and Pump for your tank. (I personally like the MAG Drive pumps)
Live Sand (Research Deep Sand Bed, Shallow Sand Bed, and No Sand Bed)

And If Im missing anything anyone else will chip in.