By using premium gas in a car designed to run on 87 octane, you will just be throwing away your money, and your gas mileage will likely go DOWN. Don't use premium unless you need to. This all holds true unless you have advanced your timing, or course. To get the best economy, use the lowest octane possible that does not produce spark knock.
As far as the OD button, leave the OD on unless your transmission is hunting. That will yeild the best economy.
As far as driving habits to get the best economy:
1)Quickly accelerate to your cruising speed (Quickly doesn't mean revving the hell out of it either, just nice smooth, quick acceleration)
2)Keep constant cruising speed.