Best way to avoid warping of ABS 3D Prints?

I always have a problem with my ABS warping on my heated print bed. What is the main cause of this, and what can I do to prevent it?

Any help would be greatly appreciated!

Most ABS warping seems to be caused by uneven or premature cooling of the print. ABS likes being printed in a draft-free, warm environment. Placing your printer in a draft-proof enclosure seems to eliminate most of the problems.