Sorry if there already is a topic/guide about this, but if there is, I haven't seen it.

I simply stayed alert while trying to fall asleep, instead of relaxing. It worked, and I went through the stages of NREM-sleep while being aware of it. I waited to enter the REM-sleep, and finally it came, and I was lucid.

I did this two times this night, and became lucid both, as a result.