It is important to have a correct approach to practice. Get one small piece of information and learn it well before going on to the next topic. Make sure each new thing you learn is thoroughly worked into your playing. This way you won’t forget it, and you can build on everything you learn. You will benefit more from several short practices (e.g., 30 minutes per day) than one or two long sessions per week.
This is especially so in the early stages, because of the basic nature of the material being studied. In a practice session you should divide your time evenly between the study of new material and the revision of past work. It is a common mistake for semi-advanced students to practice only the pieces they can already play well.
Although this is more enjoyable, it is not a very satisfactory method of practice. You should also try to correct mistakes and experiment with new ideas. To be sure you develop a good sense of time, it is essential that you always practice with a metronome or drum machine.