If you're legs are numb, you're body is falling asleep. Keeping your eyes closed would be a good idea, but try to have you're mind's eye open, the imagery will be all in your head, lol. I'm really no expert in lucid dream entrances either though, lucidity for me seems to just happen now ever since I tried binaural beats (they seem to help give you the tingly feeling). I sometimes get lucid dreams when falling asleep on my back after waking up in the middle of the night, but they tend to be nightmarish and end up being false awakenings and having some feeling of sleep paralysis.. but that's just me I guess.