This post is inspired by the "beginning of the semester pep talk" I've been giving to my students lately.
1) Plan your work.
Plan when you are going to practice. Don't expect practicing to "just happen!" Look at your planner for the week, and make "practice appointments" with yourself. (Btw, you should have a planner/calendar of some kind - paper or electronic.)
Plan what to practice. Prioritize your practice based on what needs the most attention, or what needs to be learned the soonest (for an upcoming performance or lesson). Don't just sit down and start making noise. Your time is extremely valuable; use it wisely! Don't waste all your time playing the stuff you already do well. I think it was Tuckwell who said "If you always sound good in the practice room, you aren't practicing the right things."
2) Work your plan.
Once you've looked at your planner and made those practice appointments, KEEP them! Stick to your plan, unless there is a legitimate reason to change it. (An invitation to join some friends on a Starbucks run is not a legitimate reason.)
3) Make sure some things are more important than work.
Faith, family. The best musicians I know lead full and balanced lives. They do lots of interesting things besides practice. This post is basically about priorities. Of course, to be successful as a musician, you must make your practice time a very high priority. Nevertheless, sometimes life gets in the way. And sometimes, the best thing for your playing is to rest. Be flexible when you have to.