The later type is definitely harder to stabilize and deepen. You should try to leave the dream scene ASAP during those. Do some quick stabilizing tricks such as rubbing hands, examining small objects, and etc, then leave immediately. Also try not to line up your body with the bed, so crawling on floor is a good idea. As for the darkness, transitioning to a different scene usually helps. In addition, you can also try to flip light switches. Don't expect the light to come on, but rest assured something will happen. It can be lights in the other room, lightening sun the sky, street lamps being turned on, and so on.