Distinguishing Waking reality from a dream reality is a key process of becoming lucid, you have to realise the difference between them. Reality checks are a simple process of analysing your current state of experience, doing this creates a solid awareness of waking reality.
How often do you question yourself whether you are awake or not? The answer is probably very rarely or even possibly never, a lot of us seem to be on a form of autopilot which is why we will never ask this question while we dream because we never do it while awake.
But once you have a habit of performing reality checks throughout the day, you will automatically do them in your sleep, at that moment you would most likely snap out of the dream trance and realise you are dreaming!
Reality checks rely on performing an action that either can or can not be done in each reality, for example, can you fly right now? Can you hold your breath forever? Can you walk through walls? You obviously can not in waking reality but in dreams you can. Other state tests could be simply reading a sentence, in waking reality it is very easy to do so, but for some reason in a dream it is impossible to re-read something, also math equations and reading the face of a clock is very hard to do in a dream.
So once you have realised whether or not you are dreaming, it is a good idea to really relish on this realisation, use all your 5 senses to their maximum ability to capture your current vivid state of being.
By taking true notice of your surroundings you build a heightened awareness of yourself and states of experience that helps distinguish a dream from the waking.