ISO Speed and Shutter Speed
When you are outside and it is a sunny day, your camera might be bringing in too much light. Make sure your ISO speed is set to either 50 or 100, depending on how sunny it is. Also, have a high shutter speed at around 1/640 of a second. For baseball, 1/1000 is best if you want to freeze the ball in the air. This all contributes to the photo coming out correctly and not over-exposed. If your camera has an auto sports setting, this will generally do a good job in choosing your shutter speed. The photo on the bottom left was taken at a relatively slow shutter speed, so the photo is too bright. The photo on the bottom right was taken at 1/640 of a second, so the colors are much better.
If you have just been shooting indoors, make sure the Tungsten setting is turned off and your white balance is on auto, otherwise the photos will come out blue.
Zooming and Cropping
When shooting football or soccer, the field is extremely large, so it is difficult to get photos that are not too far away. In this case, it might be best to get a 200 mm telephoto lens, which will produce much better photos since it will allow you to zoom in much more than a regular lens. These should only be used outside since they will not bring in as much light. If you do not have a telephoto lens, you should zoom in as far as possible and then crop the photo later. However, cropping can only be done if you are shooting in a high resolution. Otherwise, when you are cropping, the photo will become too small to make out. The photo on the bottom left was taken at 3072 x 2048 but was reduced to 600 x 400. The photo on the bottom right has been cropped from that same photo and has also been reduced to 600 x 400. There is less open space in it, and the action is far more obvious.
It is much easier for the camera to focus when shooting outdoors since there are more and brighter colors and the players are not moving as much in and out of the frame. However, manual focus is sometimes best when taking pictures of soccer or football since the players are so far away. You should set the focus at infinity, which then allows you to take any picture that is far away and have it be in good focus. If you have a good telephoto lens then autofocus should be fine since the players will be close enough with your zoom for the autofocus to work.
The best place to be shooting in soccer is either at the end of the field if you have a good zoom or off to the side but closer to the place where your team will be shooting the ball, instead of in the middle.
During a football game, you should simply move with the players, but be either in front or behind, depending on whether your team is on offense or defense since this will allow you to see their faces.
In baseball and softball you should stand near home plate so as to get good pictures of the batters and to be able to see the faces of players running the bases or in the outfield.