The keyword is reliability. Subliminals aren't reliable unless we are bombarded by them repeatedly. Just like commercials. I watched a movie on television last night (I rarely watch TV. The only thing TV set is good for is plugging in a videogame console) and saw the same advertisement during each commercial break. The movie was two hours, with at least ten commercial breaks. Poison to the mind, I say. And have you been to Menards recently? "Save big money, save big money" blaring through the speakers in the next isle, and constantly humming from the high ceiling. Insanity.

But I digress. Back to lucid applications. I'm no subliminal expert, but based on my logic I think that the message would have the best effect if it told you to do something. Sure, a message that said "become lucid" may get a lucid once in a blue moon, but "realize you are dreaming" may help even more (you are more familiar with 'realize' and 'dreaming than 'lucid'). Even better still is "do a reality check," "you like reality checks" or "[insert actual reality check name here]" (because this actually suggests that you do something tangible).