Say you wanted to be able to draw more accurately, then the skill you'd need to practice would be your ability to accurately judge shapes in three dimensions and translate them into two dimensions on the picture plane. With building that skill as your goal, you could think up some exercises around it and get down to some regular, focused practice.
If you just draw a lot, over time your drawing will naturally become more accurate. But if you take that skill on its own and practice it regularly, deliberately and with focus, your drawings will become more accurate a lot faster. The greater skill you now have with that particular aspect of drawing and painting will then naturally become a part of everything you do.