After several years of practice I've noticed a couple factors that affect my success with lucid dreaming. Perhaps this will help others:

1) If work has my mind absorbed with a lot of job pressures I do not LD. Only once I achieve my deadlines and can relax do I LD.

2) If I have been more physical than my seditary job sitting at a desk all day, I am more likely to LD. This is because I then stay in bed longer in the morning and rather than waking right up I keep drifting back off to sleep which keeps me in REM.

Both are also tied somehow to "intent". To intend to LD, I have to be relaxed without pressure occupying my mind, and tired enough to not keep thinking about my intent so that it becomes me trying to "will" it to occur, which is counter-productive.