(also called The Law of Repetition)
Practice is purposeful repetition, the purpose generally being that we want to improve the quality of the behavior or experience in some way.
That which we practice, that which is repeated, becomes habit.
If we practice with poor quality, then poor quality becomes our habit. If we practice with great quality, then great quality becomes our habit, and our quality improves.
When we practice being Loving, we become more Loving. When we practice being more Peaceful, Joyful, Powerful, and Wise, we become more Peaceful, Joyful, Powerful, and Wise. We become that which we Practice.
Implementation: Pick a skill that you want to improve, and practice, practice, practice! Practice with great care, focus, and diligence, and you will improve!