Lemmee see... Make sure you're doing it after a few hours of sleep (WBTB), or if you're sleepy in the early afternoon, that's a perfect time too. Sometimes entering SP is easier if you're lying on your back (this is true in my experience, but I have to actually be sleepy for this to work- otherwise I lie in whatever position is most comfortable). As for staying awake, don't do something (mentally) that keeps you too alert, or you'll never fall asleep... hmm that sounds weird. If nothing else, just let your mind wander but keep the tiniest bit of awareness and "watch" your own thought processes.
Causing it to occur faster... I've heard that if you're physically exhausted (after a run or something), SP can come on faster... but I might just be making that up, I can't remember who said it.

That's all I can think of for now, but the best advice I can give is not to get too bogged down in cut and dried techniques, just keep trying different things and go with what you think helps the most. Everybody's different. Eventually you'll strike gold, I guarantee it.