|I too have been shooting a lot of soccer for a school paper. The two biggest things I've learned have been about placement and ISO.
In terms of placement, watch where the lights shine the brighest, and watch where the action points are going to be. (Namely the goal, and the 2/3rd's mark on either side of the field.) The three best action shots for soccer involve the keeper making a stop, someone shooting the ball, and then midfielders heading the ball after the goalie clears the ball. I prefer to shoot from between the goalbox and the midfield line (for whichever team I'm covering), and then if you can get around to the back during corner kicks you can get some good results from the pile-ups.
As far as ISO goes, on your camera, cranking it up shouldn't be too much of an issue. It is better to run a higher ISO (1600?) and a fast shutter speed to freeze the action and the ball, then it is to run a lower iso with a slower shutterspeed. With the higher ISO your colors won't be quite as rich, but you'll capture more vital detail. (and avoid missing the perfect moment due to motion blur.)