Next time, as soon as you realize that you're dreaming, calm yourself. With any luck, simply doing this will prevent the black void from ever forming. If, however, it does, don't panic. Calm yourself, close your eyes, and visualize a dreamscape. If you can, spin your dream body while doing this. That should get you back on track. Just remember not to get too exicted - that's usually the cause of the ending of a lucid dream.

If you have any other questions, please ask. Welcome to the forum!