I don't know what lens or lenses you have access to, but if you have consumer type lenses like the 18-70 or the 55-200 kit zooms, make sure you keep the ISO setting up in the 640 to 800 range, even during daylight hours!
You need to ensure that the shutter speeds are high enough to freeze action. In daylight (so I assume this is maybe a jr. high or Junior Varsity game) high ISO settings will not result in too much noise with any Nikon body ever made.
Get as close as you can. If you look and act like you know what you're doing, at junior high and HS games, the officials will usually let almost anybody walk right up to the field's edge. Try to stay 5 yards ahead of the line of scrimmage and watch for action to develop. Not sure what position the kid plays....if he's a cornerback or safety that's one thing...if he plays noseguard or defensive tackle, you might want to be shooting from BEHIND the line of scrimmage, so you can see his face a bit more.
Try and keep your camera trained on the specific player you're after. Get some shots of him just standing there,before each play, or during a timeout if he removes his helmet. Try for action, but also get a few shots of the kid just within the context of a game of football. Do NOT WASTE shooting opportunities reviewing plays on the LCD....check your exposures every few minutes if the light shifts, but don't let chimping cause missed shot opps!