So you have your tank now! Whats next?
Well now you read and research what you can accomplish with your size tank. Will it be a Fish Only with Live Rock or a Reef Aquarium. The reason i say this, so you can obtain the propper equipment for the use. Get your substrate, powerheads, lights, sump, skimmer, etc before dumping tap water and calling it done!
Also look into where or how you will get RO/DI water for your system.
Lots to do!!! Have fun!