My fave subject and one which has taken a while to absorb. There are many things to consider before shooting, 1st, where to position yourself. I've found that it pays to get as close as you can to the track so that the bikes FILL YOUR VIEWFINDER. No good being too far and then having to crop later, lost pixels don't make a sharp pic. 2nd, what do you want to show in your pic?, if you want bikes leaning almost to the floor then find a sharp bend where you can get close. Shoot as the rider is close enough to see his eyes for impact. 3rd, if you feel bold enough for side-on shots as the bikes fly past at well over 100mph, then find a straight part of the circuit. Here is where you will need to hone your skills at panning with the bike and shooting at the same time. Try many dummy runs without taking any pics, it will pay off. 4th, choose a shutter speed of at least 750sec or higher if you're panning and use predictive autofocus. You might have to choose a higher ISO like 500, or 800, it depends to some extent on the available light, if it's a sunny day then you're ok. Remember my golden rule which I've found works well for me; always make sure that your subject FILLS YOUR VIEWFINDER.
To be at the trackside as the bikes roar past is truly exhillerating, and the smell of Castrol R is sheer perfume to me as it drifts from the exhaust smoke. Many of my pics show even the heat waves from the exhaust pipes as the bikes fly past. Go on, enjoy it!!!.