In my experience a week of good practice that includes work on material covered in the lesson goes well with a once a week lesson. How long that lesson should be depends on a few things:
- How much time you put in to your practice.
- How much new stuff you can handle each week. (Do long lessons leave you feeling overwhelmed?, do short ones leave you feeling underwhelmed? Does a practiced week still leave you with a feeling that you did too little?)
- How good your instructor is with disseminating information in the allotted time. (Most professional teachers have a standard of a half hour to work with for most students, and should be able to impart information within that time period.)
- How experienced you are. Experienced players tend to benefit from longer lessons.
- How much you talk. This is an important one. I have had many students who love to talk, and that talk is nice but it cuts into the lesson time and how much the teacher can convey.
Under the right conditions, a half hour is sufficient once a week. But for advanced students and those who like to talk allot, an hour is often about right. I rarely felt or wished I needed more time than an hour once a week lesson, but I did come across the rare student, or occasion where more time would have been helpful.
This interaction needs to be tailored to the students needs for the most part.
I would also note that Hour long lessons tended to create a more relaxed atmosphere, which helped my performance as a teacher.
Key to success however is the practice time you spend. Spend time practicing every day, and that will make any lesson you have better, more relevant and inspiring. The more time you spend the better. I have heard professionals say they practice 2 or 3 hours a day (there may or may not be limitations here on some instruments). That is probably enough to be really great before too long. I have had successful students (progress making) that practiced 15 minutes a day. 30 minutes a day is probably a good minimum time for a majority of teacher recommendations based on my interaction with other teachers. I tend to emphasize the "every day" part, and "work on material from the lesson" part of the discussion.
One thing to note is the timing scheduling of your practice. 4 hours one day does not equal more practice than a half hour every single day. In fact 5 minutes a day is worth more than one practice session of 4 hours. The consistency of doing it every day helps your brain, muscles, spine, and any other parts you use to form and keep memory and skill from the work you are doing.
