This reminds me of a technique my father told me about before. He said "think of something that you'll recognize instantly and will know is impossible, like a pink tree. Then, as you're falling asleep, say, 'I will dream of a pink tree tonight and know that I'm dreaming' as you fall asleep, and when you see the pink tree in you dreams, you'll become lucid." I never really tried it, but it is definitely worth a shot. I would guess whether a word or an object works better for you would just be based on whether you're more an auditory or a visual type of person.
