All of the above suggestions are nice, but the true most reliable method for leaving a lucid, including sleep paralysis is to take very deep long breaths in and out.. repeatedly, until you see the dream fading around you (usually takes about 10 seconds). The reason this works flawlessly is because the body notices any sudden changes and will awaken the dreamer... hence, this is why so many LDs fail due to being over excited.. breathing, heart rate, and other factors.. this is the 100 percent fail proof method I have used.. and it is quick. Spinning, falling back, and some of the other things suggested are typically used as methods for increasing lucidity, teleporting, or staying IN THE DREAM... and falling back, and spinning are both methods known to create false awakenings also... To get fully out of Lucid dreams, including false awakenings and SP, use this method...
If you have anymore questions about this let me know..