Practice, practice, practice. I heard this as a kid growing up and really hated it. It might have been because I did not love what I was practicing. My mom want me to master the piano, later in life I found out I had some hearing disability, that explains why I never enjoyed learning to play music. Now that I have a true passion for visual art, I love practice and encourage it. The trick is to make it fun, even an adventure. Pick up a pen or brush when ever possible and draw, doodle, experiment with color, or just light and shadows.
These are examples of taking a simple subject and turning practice into an adventure.
Working on simple tree structure, play with the light, shadow, but with unexpected color combinations. Who says the sky needs to be blue, why not let the tree be blue. Paintings these I worked on simple eye hand coordination, yet adventured into a new area of color.
Pick a simple subject and see how many ways you can change just one part of the composition.