Practice Ideas

Some miscellaneous thoughts:

Discipline and persistence are essential to successful performance on an instrument. Though beginners are not able to concentrate for long periods of time, all students benefit from more regular and frequent practice.
Find a regular time in your daily schedule that can be dedicated to practice. Before school, before dinner or before bedtime are usually better times than low energy times like after school or after meals. Post up a practice calendar and keep track of the amount or days that you practice.
The activity of practicing is not only playing through your assigned pieces; review an older pieces, work on exercises that your private teacher gave you, pick a hard spot and work on just those few notes, improvise. Practice should not be mindless repetition. Think about your posture, positions, intonation, rhythm, and sound. Repetition:
If you play a passage incorrectly. Identify and isolate the problem. Vary the way you practice the problem.

If you play a passage correctly. Great! Play it 5 times in a row correctly! (To know something on a deep, subconscious level, the correct execution must be drilled multiple times.) For more ideas on how to practice consult with your private teacher.