Practice-o-pedia  is an excellent guide for late intermediate/advanced students who wish to make their practice time more effective.

Learning Strategies for Musical Success is an excellent guide for parents and students (written in layperson’s language).

Interleaved vs. Blocked Practice discusses the pros and cons of mixing sections in practice (which provides better long term results) and practicing blocked groups sequentially (which provides short term results).

Musictheory.net offers a number of ear training and reading exercises for beginning through advanced levels.

Insidemusicteaching.com offers a number of resources (including sound for Rhythm Bootcamp exercises) for students and teachers.

The Bulletproof Musician includes a blog, and a complete program of practice for advanced musicians that includes information on managing thoughts as part of performance preparation.