Try this exercise:
Take some time off and go to a quiet place. Try being conscious of the thoughts that come to your mind. You will find that most of the time the thoughts that come to your mind are totally irrelevant to the situation you are in or some situation for which you are making some plans.
Resources :
The best books I have ever read that teache you to remain conscious in the present moment is Eckhart Tolle's "The Power of Now" and Shannon Duncan's "Present Moment Awareness".
These books have knowledge that has been collected from several sources and of course the authors seem to have practised what they teach.