I think the common thing for people to figure out they are dreaming is to be more analytical in real life. Question things if they don't make sense. If they do make sense, question why. For example, and I know it sounds stupid, but when you wake up in the morning and brush your teeth, or comb your hair, or do whatever is you do, think to yourself, why do I have to do this. Or why is the sun out today?...when I flip this light switch does it really change the light in this room? etc. those are rough examples but I think you get the point.