Fortunately, once you become lucid, it's not hard to add other rational thoughts.

Write down one or two small lucid dreaming goals (flying). Focus on one at a time, and only one (until you achieve that goal). Review this goal before bed, and during any WBTB sessions you might do. Hopefully, the idea will stick, and you will remember once you become lucid. Patience is key--it might not happen on your first try!