Get plenty of sleep the night before, try to get some form of aerobic exercise daily, start working on whatever task you need to focus on within 30 minutes of d

Get plenty of sleep the night before, try to get some form of aerobic exercise daily, start working on whatever task you need to focus on within 30 minutes of dosing (ideally before), stay hydrated, turn off notifications on your phone and block addictive sites, wear noise cancelling headphones. If you're going to listen to music have it on random shuffle so that you don't have to break focus to change the music yourself.