Try asceticism and meditation.
A good book on meditation is The Mind Illuminated by John Yates.
Try praying 5 or 15 decades of the Rosary every day as a meditation.
A good way to start asceticism is to try and not commit any sins by keeping a sin journal.
Also try reading Outwitting the Devil by Napoleon Hill there's an audio-book on YouTube.
Some would argue, what defines us is habit. If you want to change, learn to control your mind and form powerful positive habits:
1. Changing a habit is simply making yourself conscious of it and then avoiding it by thinking or doing something else instead the instant you find yourself doing it.
2. Creating a new habit is as simple as spending 5 minutes on it every single day, never missing a day, and watching as you slowly start to invest more time into it.
3. Use your powers of introspection, what's triggering you to think/do something with Pavlovian response. Write these down and find ways to avoid these scenarios.
Now there are two parts of the mind: conscious and subconscious. The subconscious has full control of your body and all physical senses but has no self determination, it only does things depending how impressed it is by them. On the other hand, the conscious mind is powerless but contains your conscious will. Your subconscious acts as the proxy between the environment and your consciousness. The only thing which allows your subconscious to act according to your conscious will is how well it can impress your subconscious over the impressions it receives from the environment. How this is done is by your conscious mind creating an strong intention and holding it until the subconscious conforms. This intention must be more vivid than that of the environment otherwise it will not work.Post too long. Click here to view the full text.