Find a book, newspaper, magazine, or any other reading material: When you are lucid dreaming, the part of your brain in charge of recognizing numbers and letter is still asleep. If you have problems reading text, or read it once and when you try again it is different, then you are most likely dreaming.

Turning the lights on/off: When you are dreaming, one of the things that you are unable to do is adjust the light level of the settings you are in. If you try to turn the light switch on/off and nothing happens then there are 3 possibilities:
1. You are dreaming
2. The light bulb burnt out or 3.The light switch doesn't work for some reason.

Trying something considered "impossible": Another method to test whether you are in a dream or not is to try somthing that you know is impossible in the waking life. Commonly used examples of this are: Putting your finger through your palm, crossing over through a mirror, levitating, etc. I suggest you don't try something like flying out your window or such...just to be on the safe side