What I like to do, is as soon as I become lucid, take slow deep breathes (synchronized with my actual body) this helps me remain calm. Too much excitement can cause you to wake. I then like to do a reality check. This helps stabilize and clear up my surroundings. I find that spinning works better once you have been in the dream a while and then it starts to fade. Like Jeff said, paying attention to detail, and actually feeling your surroundings with your hands can also stabilize the dream. Also, if you are thinking/worrying about waking up, then this can cause you to do just that. I used to have that problem early on, but I like to get involved with dream activity as quick as possible so I don't think/worry about waking up. Good Luck!