I think success comes with a bit of both types. Daydreaming and a passive desire for lucid dreaming I think are necessary, or else you would lose interest. As for more forceful intent, I think it's best if it is narrowly focused and clear. If you have a broad, vague intent that you express strongly ("I really want to have a lucid dream!") then that's the kind of thing that can stress and discourage because it's difficult to measure or see progress. It doesn't call you to a specific action. Instead, you want to direct that intent into something more concrete ("When I walk through a doorway, I will perform a nose pinch reality check.")

It's an interesting topic because I think people uses mantras for both purposes, but if they confuse the two then they may be counter-productive. I think some mantras are meant to be more passive ("I dream"). Repeating it over and over doesn't so much set your intent but rather puts you into a sort of hypnotic state. On the other hand, a more specific mantra sets a clear intent, like LaBerge's original ("The next time that I am dreaming I will remember to recognize that I am dreaming.")