Practicing is the most important part of mastering any worthwhile skill. I can try everything in the lessons but if a student doesn't practice, they will not be able to reach their potential. A good rule of thumb is to practice for the same amount of time that your weekly lesson lasts. If you have a 30 minute lesson, plan on practicing 30 minutes. In each lesson, I write up a practice chart with instructions on how to complete each task. Following this practice chart will be the best way to progress quickly and efficiently.
10 minutes of practicing every day will always yield better results than practicing for 12 hours once a month. Consistency is key. While playing for the same amount of time as your lesson (or more) is optimal, at least play something every day.
While all of these things are important, the most important part of effective practice is focus. Practicing with a distracted mind is not going to improve technique, musicality, memory, or any aspect of learning a musical instrument, and can actually cause the musician's skill to be worse. I believe that short, consistent, focused practice sessions are the most effective, and try to teach my students how to practice in this fashion.
In addition to the practice charts and music books we use, I will now start using these online resources as a tool for teaching as well!
The Drone tool is a great tool for any passage that is in the higher register of your comfort zone, and passages in which the intervals or chords are hard to hear. I ask that my students use the a drone when practicing scales, as it is easy to modulate into another key especially in two and three octave scales. This is also a good tool for tuning your instrument as well!
The Metronome tool helps develop a precise sense of tempo and rhythm. Using the metronome when practicing scales helps to increase the speed and accuracy at which they are played. In addition to scales, I ask that my students use the metronome when working on sight reading exercises as well.
My Listening tool is not yet ready, but I plan to make a YouTube playlist of Suzuki book 1-2 recordings that are good quality. Listening to pieces is one of the most important parts of the learning process, especially in violin, and is significantly increases the speed by which students can learn and master pieces.