I have had an issue with this too and I’ve struggled with it for about 2 years. My tips: You have to sleep at least 6-8 hours every night and eat 3 meals a day, and drink water (a lot). Always write down all the work you have to do and keep your workspace clean and organized. Listen to relaxing music while doing your work and the most important one is to take breaks every 30-40 min of doing your work. Set a reward system (for example – buy candy and after every work you finish, reward yourself with it). Put your phone on silent mode so you don’t get disturbed.