Regardless of the instrument you play, there are several common aspects to developing a successful practice routine. You will benefit more from several short practices (e.g. 15-30 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 and because the muscles involved in playing the instrument are still developing. It is also important to 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 may be more enjoyable, it is not a very satisfactory method of practice. You should also try to correct mistakes and experiment with new ideas. In order to develop a good sense of time right from the start, it is essential to practice regularly with a metronome or drum machine.