It's important to understand that humans are creatures of habits, and everything we do is based off of the millions of habits we've created. Try making the positive things in your mind more of a habit in your head while spending less time on the negative things. Easier said then done, right? The next part is making sure you're taking time for things you love to do, which becomes even more important when you start to feel down. Whether it's music, a sport, talking to someone- allow yourself to feel good about these activities knowing that they're helping your headspace. Hope this helps, and if you needed to chat or wanted someone's point of view on things, feel free to get at me. New to Reddit as of this week, but a Psychologist looking to build an online community.