1. Right before you crash, down a cup of java. The caffeine has to travel through your gastro-intestinal tract, giving you time to nap before it kicks in.
2. Close your eyes and relax. Even if you only doze, you'll get what's known as effective microsleep, or momentary lapses of wakefulness.
3. Limit your nap to 15 minutes. A half hour can lead to sleep inertia, or the spinning down of the brain's prefrontal cortex, which handles functions like judgment. This gray matter can take 30 minutes to reboot.