1. Know what you want to accomplish. It can be very simple, playing a scale more in tune, or learning a measure or two of a piece. Or more complicated, but have some idea of why you are practicing.
2. Give yourself enough time. It does depend on what you want to accomplish. It will take less time to play a scale than a piece (usually), but time is important. Also repetition. Finding a time every day is recommended. If you can't find time every day, try to keep the same time weekly.
3. Be patient with yourself. Learning means change. We don't like change usually, so be patient, and know that it will take time.
4. Slow it down. Whatever you are doing, play it slow first. If it will need to be fast later, know that, but play it slow 10 times, then make it faster. The 10 times slow is programing in a way.