They are positive thoughts combined with intent. Gary Zukav talks a lot about intent. Intent gives our thoughts a goal to work towards. It boosts some extra positive energy into the mixture, as well. It's that plain and simple.
Visualization is the icing on the cake.
When you have a thought, and you intend for that thought to be brought into your life, and you can see yourself having that in your life, you will have it. Imagine that you want to lose 10 lbs. Then you decide to walk for 20 minutes each day, so you must really intend to lose the weight. And, when you look at yourself in the mirror, you imagine that you see yourself having lost those 10 lbs. If you can follow this simple process from step one to step three, you will lose 10 lbs.