I draft regularly. Some basic 'rules' I follow:

Know the road ahead.
Draft behind the the part of the vehicle's wheels if you're concerned about surface hazards.
Pop out and check the traffic light cycle.
Do it in light traffic, where random reasons for the driver to nail the brakes are reduced.
Always cover your brakes and keep you exit open.

Really, it's just a matter of understanding the risks involved, much like anything else.