This approach helps me learn the quickest:
1. Get a teacher in the beginning.
2. Always practice with a metronome, even if you are a drummer.

3. Practice for 15-30 minutes intervals, with 5 minutes breaks inbetween.
4. Warm up before you practice, either using standard warm ups, (scales, arpeggios), or playing some kind of groove that uses all of your fingers.
5. The point of practicing is to get better. You will not get better by playing the same C Major scale for the entire time. You will also be wasting time by noodling around. Practice what you can't play.
6. Practice in a progressive order. If you can't play a major scale, how can you construct major chords? Learn the easy parts of songs first, then spend the real time on the difficult ones.
7. Practice consistenly, every day if possible.
Hope this helps
