The other day I went and did a little photography class that explained the basics of photography (shutter, aperture, exposure, focus, ISO, white balance, and how to adjust them with your camera). It was awesome! I know you might not have time etc to do one, but if you have a DSLR, well worth it! Then you can half understand what Jan & PJ is saying

But, until now (I hope!) I've always taken action pics of horses on auto mode with zero photography knowledge and they mostly turned out ok. This is what I'd do:
Have it on the running man/sports mode.
Put your focus point (when you half press the button to take a photo, a red light or squares or something shows up in the viewfinder??) over the dog. It should be in AI SERVO mode, so as the dog moves it keeps on focusing, as long as you have the button half pressed.
Follow the dog with the button half pressed so it keeps focusing and at the point where you want the photo, completely press the button. You can hold the button if you want a quick series of photos. Mine only does 3 per sec, so I was better waiting for the moment I wanted and capturing that (so just after take off over a jump etc) otherwise I'd just get 3 crap photos.
Hope this helps!
Once you've mastered that you will want to know how to do it better! Trust me it happens
