Understanding that your thoughts determine your environment and that you can command your thoughts is the first step. But committing to a daily routine of developing mental and emotional strength is something else entirely. It takes discipline, character, and patience. The idea that we can just manifest what we want is a little misguided. The fact is that you may have spent the last 30 or 40 years anti-manifesting.
Focusing on worry and stress, eating the wrong foods, in toxic relationships, with limiting beliefs that have been with you since childhood. These are not removed overnight. It can take years to rid yourself of certain thoughts and ideas, and you have to be constantly vigilant about what you are thinking and what you are consuming.