Learning a new skill that requires hand-eye coordination and/or mental processing can improve your brain. I did a term paper on it in school. The trick is, you have to keep learning new things to maintain your gains. The scientists in this study used juggling as the skill they taught, but it could be any skill. I’m currently part of a study that uses brain training games to improve cognition and social functioning in schizophrenia patients. It’s great.
It’s also important to note that recent studies show that gray matter loss is due to psychotic episodes, not the medication. So the best way to prevent it is by staying on meds and staying stable!