I hope Guy doesn't mind me linking to some of excellent work.
Here is DSC member Weagi showing how it's done:
http://www.copeimages.com/Galleries/...38_DSC0064.jpg http://www.copeimages.com/Galleries/...38_DSC0029.jpg The sole representative of Team 3UpRacing:
http://www.copeimages.com/Galleries/...98_DSC0041.jpg 
And here an unlucky lad showing what not to do (great shot, though):
http://www.copeimages.com/Galleries/...14_DSC0006.jpg