When you are in your dream and THINK your dreaming, plug your nose. If you can still breathe than you are most definitely dreaming. In real life there is no possible way you could breathe through a plugged nose. Take that opportunity to do anything you want. You need to really believe that it is a dream, otherwise you are risking losing your lucidity. Start out by doing simple things, such as jumping really high for an unrealistic suspended amount of time. Just push the boundaries slowly, that way you still have the confidence to try bigger things and you will really believe you are in your dream world so it will come easier.