Ok, here are the rules:
1. Use a monopod or hand hold so you can quickly change composition. A tripod is useless.
2. Shoot vertical 90% of the time and use a focus point in the top center, around the face of the player.
3. Use Al Servo focus and IS.
4. Use aperture priority mode, with the camera set at f2.8 if it's low light. Try and get some more depth of field at f4 or f5.6 if there is enough light. If the light is constant and not changing, you can lock your exposure in manual mode. You need at least 1/250th shutter speed but 1/500th or 1/1000th is even better. 1/500th will stop the action.
5. For soccor, shoot behind the end zone. You can get the action coming up the field toward you. With the 400mm lens, you will probably be too close after they cross the 50 yard line toward you. That's when you pick up your 70-200 if you have one...
6. With a full frame camera, 400mm is perfect to get the action on the other end of the field. With a crop 1.6x sensor, you essentially have a 650mm lens. That's just too much for sports unless you can shoot the action on the other end of the field.
7. Shoot in high quality jpg mode instead of raw. You can get more burst with it and shoot like 60 shots before the Canon 40D slows down. With raw it can only shoot 16 burst pictures before stopping.
Good luck. Here is a little something from my past to give you inspiration... The great Ryan Leaf against Michigan in the Rose Bowl. Michigan won and went on to capture the national championship. Ryan Leaf, well, we all know how his career ended up.
