The moment you notice your vision fading at all, do the hand rubbing and start spinning. Even if you feel like your awake, if you can still feel your hands rubbing together, you can pull the dream back. Here’s and example of one of my own personal experiences with saving a very unstable dream.
Also, Sandra wrote a great article on our knowledgebase call Prolonging Lucid Dreams, and I would really recommend you check it out.