I'll keep this short and to the point.
Last night I got some descent sleep, did my WBTB and even used my normal dose of G. No lucids. That's pretty unusual for me. Missing is pretty rare, especially with supps.
However, I have noticed something that is worth sharing, and I will bet others can benefit from it. When I do a lot of last minute planning on what I will do while lucid, or what I will do (i.e. I'm a bit de-focused and non-committed) my lucid dreaming suffers and I might even miss. I have noticed this enough times to extract an obvious pattern.
When I am very focused and have a well defined set of goals or conditional goals, AND I am not second guessing anything, I almost always succeed.
Point - be confident, be focused and have a well defined plan going in. I think this general statement would be true of anyone, regardless of relative level of dreaming or lucid dreaming experience.