The main things I find are using the appropriate shutter speed for the shot, focus and location. For an action shot like the one below with the wheel in the air I had it set at 1/1000 sec. because I wanted to catch that moment, but it doesn't work so well for the shots of someone cranked into a corner because they don't look like they're moving that fast.
I found you could get away with around 1/250 to 1/100 sec. to get the motion blur of the background but still get a clear shot of the rider. The tricky part is panning with the rider so you get the effect right.
Get used to the shutter delay on your camera, and if possible set your autofocus on the spot the rider will be in when you take the shot before they get there. That way the camera isn't busily trying to autofocus while the rider is long gone.
Play around with a few different locations, inside and outside a corner, trying to catch them at maximum lean, a high spot above the corner looking down on a group works well. Bikes coming over crests look good too.
I still have a fair way to go, but the practice is half the fun

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