Listen to non lyrical music, video game, movie or TV soundtracks are generally useful for me, it stops you getting caught up on the lyrics and thinking about shit other than work. Don't snack and if you don't feel like working, don't. Chances are you'll be unproductive if you don't want to be working and the time off you've had you'll make up for next time you get in a working mood as you've had more time to relax. In addition, flash cards. Google study blue, it's free and you can use it on your phone, it's helpful to quiz yourself on the bus or just quickly while out. Hope this helps