Focus for shorter times. Rewards like reading or watching your favorites. Take the evening of, just relaxing. Which you sometimes don't allow yourself when working for yourself
Sticking to a program or plan. If I have a general idea of exactly what I should be doing, it's easier to focus. But that works for me because I am goal-oriented. I suggest you figure out what kind of person you are cognitively and behaviorly, then you can look into what typically works best for your very special and unique brain!!
The best focus technique I have found which works for me is either a meditation, or a stepping away from whatever I’m doing to just think and reorganize my thoughts to the task at hand. 5 minutes away (short walk, or bathroom break) can go a really long way helping me to focus