I dont think you can do it too much. The trick with reality checks is to genuinely question reality.
Its very easy to go "Am I dreaming? Hmm, no" but the most important thing is to think about the question, take a moment to look around, check things are as they should be, consider the possibility that this could be a dream.
When you are dreaming, you will think "That flying banana looks completely normal" You will not even consider it to be a dream. If you have got into a habit of doing reality checks without really thinking about it, then you will probably one again do a RC and not even realise.

The more you do it, the more chance you will do it in your dream, but its the way you do a reality check that is important.