That's the funny thing about RCs. They only work on an "instinctual" level, and you're not lucid until after you perform them. So you have to hope the habit transfers into the dream. But seeing as how the chances widely vary, I never rely on it.

Better to use intent, is what I say. I think it's more likely you'll have a dream related to your intentions, than a random dream which may give you the chance to do a RC. But you have to be convinced your intentions actually influence your dreams, otherwise your mind takes it as an empty suggestion.