One of the biggest challenges for young musicians is learning how to practice. It isn't just pulling out your instrument and playing through the music you have. Practice should always involve goals like what you want to improve on, and what skills you want to master.
SCHEDULE
Schedule your practice time like you schedule a doctor's appointment or a soccer practice. When you leave it up to a what time opens up, it often is the first thing that doesn't get done.
MAKE GOALS
Make goals for what you want to accomplish. Both short-term and long-term goals are helpful. When you write them down and hang them near where you practice, you are reminded of why you are doing this.
USE A METRONOME
Practicing with a metronome helps you keep a steady tempo and can alert you when you are miscounting rhythms. Don't be afraid to start at a slow tempo; it's always better to do something slowly well rather than something fast inaccurately.
SCALES
Scales are a wonderful way get warmed up. Focus on your intonation, your tone quality, your technique, just about everything!
START LIGHT
Sometimes the hardest thing about practicing is just opening your case. Tell yourself you are just starting with 10 minutes, and then gradually increase your practice time day by day. A good goal for most elementary school-aged students is 30 minutes daily, at least 5 days a week.