the first thing you need to do is look up and read about cycling a tank if you haven't already done so
the second thing is considering how you want the tank to look, my personal taste is getting some black matte Krylon Fusion paint for plastics and painting the bottom and back with a few coats and using Flourite black sand as substrate with some driftwood
Also, please take time in considering the type and brand of filter and heater you will purchase (I recommend Rena Filstar xP3 and Visi-therm Stealth 250W heater for your setup). If you want some water movement or surface agitation I recommend Maxi-Jet pump/powerheads.
A thermometer wouldn't hurt either. I don't trust stick-ons with tanks that have thicker glass like 75s, the Coralife Digital Thermometer would be great for a 75.