If you haven't bought your tank yet then here's a few tips.
1) Go as large as you possably can!!!!!!!! Bigger is better with Oscars. If you want to house an Oscar with other fish then 90 gallons or larger would be ideal. A 90 gallon would also require smaller "room mates."
2) Over filtration and moving water is key. You will want alot of filtration and possably a power head in this tank.
3) Add all the fish at the same time so that no territories will be established.
4) If adding Green Terrors or Jack Dempsies then make sure they are smaller than your Oscar or they will beat up on him.
5) Properly cycle your tank. Don't get overly excited and throw your fish into an uncylced tank. They WILL die.
6) To save yourself a headache make sure your tank is lightly planted(if at all) with fake plants. Oscars will tear them out. It's a promise.
7) If you want a nice looking tank then Oscars aren't for you. Thye will redecorate your tank and they wont have the same fashion ideas that you do. In Oscar tanks the Oscar is the center peice and he will make sure he is the prettiest thing in his tank. Even if that means destroying everything else.
8) Make sure your tank is completely covered. Oscars will jump right out of the tank and on to your floor if they can.
I hope this helps. Oscars are awesome if given the right home.