Yes, awesome question, and awesome advice.

I generally advise students to have a short-list of specific projects they are working on. It could include a song or two, a scale or two, or any other topic of musical study.

After doing some warm-ups and playing a couple of things loosely just for the fun of it, then you go to your list and work on your projects one at a time, focussing on what exactly each one needs to keep it moving in the direction of being smoother, better-sounding, and more relaxed and second-nature.

Be sure and make notes of any discoveries you uncover in your study. ("Oh! I realize if I angle my wrist slightly differently when I go for this particular reach, I get better tone!" Write it down: "remember wrist angle")

Give each project as much time and focus as you have to spare, then finish up your session with playing another couple of free and easier things, just for fun.

-Lisa