Here I think I can go commercial- check out my site. The practice recommendations in it are from Chris Robertson's book, and I think they are excellent. He advises taking several practice sessions in a day, practicing for range, strength, sounds. He is an excellent player, coach, and teacher.
I have always found- practice smart. Pick on the hardest things, and the easier ones get easier. Find out how you practice well. When I went back to University to finally get my B.Mus and B.Ed, I was with a dozen players from the orchestra that I conducted. I had only about 2 hours a day to practice, while they had about 6, and I was determined that I would do my best, and stay ahead of them it I could. I found that I worked best in 3/4 hour segments, and that after that, my results went downhill quite quickly. I would practice 3/4 hour of my alloteed practice time, work on one assignment, work on another assignment, work on maybe another assignment. Then the practice rooms were almost clear, and I could practice another 3/4 hour. Then on to teaching my own students, and back to more studying. I found I could work efficiently for huge periods of time if I just kept to the 3/4 hour figure, and feel fresh and able to concentrate for each one. As I spent more years in school, I was able to make that figure approach 2 hours, but I would always stop when I found I was not doing my best, and go on to something else that needed to be done. I learned the value of practicing things slowly to eliminate mistakes first, and speeding up when I really knew what I was doing, and picking on on small hard thing and solving that, so I always felt that I was improving something in my practice sessions, no matter how whort the time available.