If you want to think positively and not negatively, I have no idea how you could do such a thing. Every person I have met has positive, negative and neutral thoughts, not necessarily in any particular order or theme. Since it is obviously not you that controls your thoughts, the whole idea of creating positive thinking alone, or dominantly, seems to be a non-starter.

If you were the owner of your thoughts you would ensure that you only have happy ones. In practice they are very mixed, so obviously it is not you that is the owner of these thoughts.

Maybe thoughts are just part of your biology. Just as blood flows in you veins, so thoughts flow in your mind, always assuming there is even such a thing.

Meditation

Meditation, on the other hand, is something entirely different. Through meditation, through natural nondual awareness, your inner peace of mind and happiness become independent of whether you are experiencing positive, negative or neutral thoughts at any moment. You become a kind of pure witness to all your thoughts, with no preference. Just as day and night follow each other, so do positive, negative and neutral thoughts. They just happen, a natural process.

Enjoy your thoughts. Enjoy your life,
Jonathan