The main thing you need to worry about now is your tank - these guys need 55 gallons for a baby (don't let the small size fool you) and 75 gallons for an adult (and that's a small adult). They also need exceptionally good filters - you'd be looking at a large external filter.
If you don't have a tank big enough, return the fish.
Food wise - they need a really varied diet. Flakes don't really cut it. They need live/frozen foods (bloodworm, brineshrimp, daphnia, etc), veggies and a good staple (high quality flake/crisp and/or cichlid pellet). Feed them a good mix throughout the week.
All fish appreciate somewhere to hide away, but big fish need big caves. Plants are great but oscars are known to uproot them. I'd stick with large, natural decor such as aquarium safe stones and bits of bogwood.
How big is your tank? Do you have the fish yet? Have you cycled your tank, and if so, how?
