One of the biggest challenges to achieving BIG lucid dreams is maintaining stability.
By stability, I mean maintaining a strong lucid presence in the dream. Because of the huge Aha! moment when realizing you are in a dream, an excitement will take hold of the novice which causes waking up, and the end of the lucid dream – usually seconds after it begins. This is usually the case in both spontaneous/unplanned lucid dreams and also for the desired/yet-poorly-planned-for lucid dreams. Proper preparation involves knowing how to stabilize the “dream body” so that you neither wake up nor fade back into ordinary dreaming.
Not really a problem. Certain “physical” movements and mnemonic techniques can vastly increase your chances of staying tethered to lucidity. The first method is described by Dr. Stephen LaBerge, and many lucid dreamers, myself included, can testify to its efficacy. This stabilization technique requires for you to spin-around in your dream-body like an ice-skater or a Sufi dervish dancer, dreidel, or maybe just a silly child. Usually my spinning was very fast, much faster than I can spin my real body around on regular ground. Something about the motion increases your lucidity, making your perception brighter and your knowledge of being in a dream more permanent. Also, interesting to note, your environment might change after the spinning from what it was pre-spin. Sometimes there will just be small changes: One time I spun around after becoming lucid, and it was dark outside through the windows prior to the stabilization, but light afterwards. You can use this peculiarity of spinning to focus your mind on appearing somewhere particular after spinning.
Another stabilization technique is to rub your hands together. Doing this at the beginning of your lucid realization and occasionally throughout the dream will help to maintain both perceptual vividness and lucidity. But maybe you need your hands for something? A third stabilization technique you can use, and you should probably combine it with the other two, is repeating a phrase out-loud such as “Lucidity Now!” or “More Lucidity!” or something like this.
Movement is the key
There are numerous other stabilization methods, but I’ve found that the above techniques work best. The real key seems to be movement. Conscious thought, all thought, is available to serve physical behavior. Movement of the skeletal muscles by will, or feelings of movement – proprioception – trigger a heightened awareness. Lucid dreaming is sometimes preceded either directly or in earlier dreams by intense movements – being chased or falling, flying, roller-coaster or wild driving, even spinning around like on a rope. If you can relax while primed for a Waking Induced Lucid Dream (WILD), you may be able to consciously visualize yourself spinning around and enter lucidity directly from falling asleep.
Remember, this is easy to forget. It is easy to forget that you are in a dream. Do what you can to maintain an awareness of the virtual reality of your situation.