Practice regularly and consistently
Practicing at a regular time for a sustained period 5-6 days per week is much better than practicing occasionally or the night before the performance/test. When you practice you are establishing and developing habits of breathing, fingering, articulating, and music reading. These habits need daily reinforcement and maintenance. 20 minutes a day, 6 days a week is much better than two hours all in one session. If you are serious about studying music beyond high school, you should be practicing a minimum of 30-40 minutes per day six days per week.
Have a specific time and place to practice
Just as you would do with homework for your other classes, establish a regular time and place to practice. Practice in an area where you can avoid distractions and interruptions. If you practice at school (ie: during tutorial or an open period) use a practice room if at all possible. Above all, make your practice time consistent and focused.
Practice makes permanent
The old saying the “practice makes perfect” is not true! The reality is that practice makes permanent. If you practice mistakes, you will learn them and they will be difficult to fix. Remember that “perfect practice makes perfect!” Practice correctly without mistakes, even if that means going very, very slowly. When you make a mistake, mark it with a pencil immediately (ie: write the counting, accidentals, fingerings, etc). DO NOT PRACTICE MISTAKES. It may take a few days to perfect something, but a patient, systematic approach will make your learning more lasting and will leave less to chance when it come time to perform.
Make something better
Make sure that when you finish practicing, you can claim that some aspect of your music or technique is better than when you started. Making one thing better, then reinforcing it in the days that follow will produce better dividends than just running through things on auto-pilot.
Divide your practice time among the following areas:
Warm-up: around 5 minutes of long tones, lip slurs, and techniques exercises. Focus on breathing deeply and producing a beautiful TONE.
Scales/Technique: about 5 minutes of scales (major, minor, chromatic, or jazz scales). Spell the scale as you finger through it. Think note names, not just fingerings. Use different scale patterns, articulations, and rhythms. Focus on TONE and work to build range, speed, and fluency.
Band Music: Master your part. Find a spot you are struggling with and break it down into small chunks. Can you count it? Do you know all the fingerings? Can you sing it? Can you play it with a metronome? Work diligently to perfect the excerpt, even at a slower tempo if necessary. Review, review, review!
Solos and/or method books: if you are studying privately, your teacher should be having you work from one or more books and/or solos. If you do not have a private teacher and would like some new things to practice, see me for suggestions!
Review, warm-down, and clean instrument: run-through any material that you worked on, warm-down with some long tones in the lower register, and swab/clean the instrument