You are just 20, you have 5 years till you tap into adult neuroplasticity. Which is a fantastic thing! Your brain is malleable now which means any habit and behaviour you develop now will stay for a very long time. Changing them after 25 will be tough. So develop good habits, exercise, run, meditate etc. Focus on behaviours rather than thoughts. Increase your productive hours and don’t allow yourself to give up. Keep your phone aside. Step out in the sun for for runs or walks preferably in mornings. Stay away from technology post 10. Sleep well. Balance your dopamine. Eat and sleep on time and eat healthy. I’m not just whipping it out of my rear, it’s actually proven. All these things.