1) With most sports, a good starting point for your shutter speed is a minimum of 1/500th of a second. However, it may need to be even faster depending on the actual speed of your subject. The motion of this professional snowboarder was completely stopped at 1/3200. While 1/1000 would also have been effective, I wanted to make absolutely sure that even the arms would be frozen as they swung out to the sides. In order to achieve such a fast shutter speed, I had to raise the ISO which brings us to the next tip.
2) Many photographers I speak with are very hesitant to raise the ISO for fear of adding "noise" to the photo. This decision is actually doing their action photos more harm then good.
The truth is, on today's entry level DSLRs, you can safely shoot up to ISO 1600 without adding an unacceptable level of noise. These higher ISOs allow you to shoot with a faster shutter speed which is Tip #1 above.
Still not convinced?
Would you rather have a tack sharp subject that's completely frozen with a little bit of digital noise...
...a blurry subject in a photo with no noise?
I'll take the sharp subject every time!
The goal is to get the shot right in the camera at the time of the exposure. Should there be a little too much noise for your liking, it can be cleaned up afterwards in post production. Noise Reduction is easy to apply in Lightroom, Aperture, and Photoshop. There are also third party plug-ins like Neat Image and Noise Ninja.
3) Lighting at sporting events is notoriously poor and flash will rarely reach the subjects. After applying tips #1 and 2, you will likely find that the shot is too dark. Don't panic and slow the shutter down. A better option is to use your widest possible aperture. If it's only f5.6 you may need to go back to tip #2 and raise the ISO even further. Ideally, you want to open up to f2.8 or f4. These wide apertures will let in a great deal of light quickly. There is also one more terrific benefit of shooting action wide open, the shallow depth of field. The background is often just as important as the subject. Distractions in the distance can really ruin a splendid moment. A very wide aperture will blur that background, and bring the viewer's attention to the subject.