The way I understand it reality checks work by doing things that happen differently in the dream world rather than the real world. For example they say that if you read something and then look away, the next time you look back it should read something different if you are dreaming. A few reality checks can be things like; jumping as high as you can, asking yourself if you are dreaming, reading something and then read it again, blinking. All of these things happen differently while dreaming and should be a "wake up" cue that you are in fact dreaming if done during the dream. Thus it should induce lucidity.

Does anyone have any other good reality checks, I'm sure I have missed a few.