Research and find out what fish you would like to keep and see if they are compatible then see if you have a place to put that size of tank. http://www.liveaquaria.com/product/a...s.cfm?c=15This
is a good site to look at fish and what they need The bigger the tank the easier and more stable
For a first tank the larger the better more room for error. Only bad things happen fast in saltwater aquariums. This is a guide to cycling The (almost) Complete Guide and FAQ to Fishless Cycling
The list of equipment will vary in the type but be similar like the light you will want at least 4 T5 bulbs if you want a reef only tank and you can get by with 2 T6 bulbs on a fish only tank. The care if very similar.
This is a guide to things you might find in your tank Live Rock Hitch Hikers
some people freak about the smallest things and I say stay with freshwater until you are comfortable putting your hand in a tank of the unknown.
There is 2 things that I find very important a refractometer and a test kit.
Go big, slow and research is the 3 things that need to be done to have a beautiful tank.