There are several points to keep in mind when one is attempting to lie. A bad liar is just embarrassing, where as a good liar can be quite entertaining (particularly when you know the truth). The best lies are usually incredibly simple or terribly complex. Simple lies are easiest to get away with; stick close to the truth and don't embellish or create detail that might be forgotten. Too much detail, especially when it is offered without being asked, reveals too much thought on the liar's part. The terribly complex lies are more entertaining, and often work because the victim can't believe the liar would put so much effort into a lie or make it so bizarre.
Keys to successful lying: Maintain eye contact. Pause before you lie, but not for too long; an immediate lie sounds planned, and a lengthy wait indicates you are making it up. Give one lie to explain a situation, and stick to it. If it becomes necessary to change the lie, make a new one which is more embarrassing (this will be more plausible because it explains why you lied the first time). Lie occassionally about inconsequential things, just for the practice. It's fun!
Lying is part of my job.