filtration and food variety would be what I would tell him.
I have 2 oscars, green terror, pleco, 2 pictus, and a couple small Silver dilalrs that will be transplanted possibly sooner or later...in a 125.
They are all still juvies with the Oscars being 6-7 inches already in the 6 months or so i have had them. They swim together nonstop and have yet to fight each other though they do put the GT in his place at times.
Nonetheless I have an XP4 and an FX5 running on the tank. I poop vac it every other day (maintly due to the pleco) and do 2 25% water changes a week. My water is always pristine and the fish seem to relish in that. When I go on vacation though I instantly see a slight change to their behavior and water quality in only a few days which just further shows their messy nature.
Food I feed pellets mainly but they also eat my shrimp pellots for the cats, algae tab for the pleco, micro pellots for the SD, anythign throw into the tank. LOL. I suppliment their food with live guppies I breed in another tank as well as tubifex worms, blood worms, beef heart, and occassionally tilapia. Food variety and water quality is crucial for Oscars to not get HITH.
Fun fish though with great personalities. Here is a video of my fish from back in Oct
http://www.youtube.com/watch?v=77F07WDS-ro