My experience is in establishing new behaviors and changing habits. The trick is to think about the circumstances where you do best, then recreate those circumstances to practice and perform in. You might want to "clear your plate" by getting home from school and spending an hour or so getting your responsibilities out of the way. Then eat, take a shower or bath, put on "performance clothes" and the shoes you might wear.Arrange your "stage" -- a stool and microphone (it doesn't have to be plugged in.) Set a timer to last about the length of time of a set. Think about starting with a song that is easy but invigorating. Then add the rest of what you want to play. When you run into a difficult part (timing or fingering or whatever) practice just those few bars about ten times, then incorporate that into your whole song. Recreate the same steps, as many of the conditions as possible, every time. This doesn't mean you can't change things for the better or shake things up, but try a basic routine, including clothes and shoes.