Although this is a very simple tip, its one that has taken me a while to learn in Dream Control:

Wait.

I don't know what it is, but whenever I go lucid I get impatient. Maybe 'cause I'm scared I'm going to lose lucidity, or because I'm worried that it may be my only lucid dream for a while, but what I've found is that if I just wait a few moments, my wishes manifest.

Example:
One lucid dream I wanted to speak to someone I hadn't seen in three years, and I kept saying to DCs "I know she's here, where is she?" and I started to lose lucidity, but sure enough, after a minute or two she came down the sidewalk. I guess there's some sort of buffer in the Dreamworld, and we have to learn to be patient.

Gee, I guess after all that typing, my tip wasn't as quick as advertised. Ah well.