alt Hacker NewsSet a timer for 20 minutes, lie down (or at least close your eyes) and force yourself to stay motionless until the timer rings. Try to let your thoughts float freely... Sometimes it works, sometimes it doesn't, but you should try at least a few times. (And yes, maybe limit yourself to just one coffee in the morning.)
I try, but apart from the coffee (I usually take two, probably the second one interferes with my nap), I think it's the lack of consistency/practice what's making my napping difficult.