Something I have noticed about most art classes that I have taken is that people focus way too much on shading. So before you begin to use painting, my strongest recommendation is to practice contour lines.
Contour lines are the edges of the piece you are trying to create. Say for instance you are trying to draw a banana. You look at the banana and see all of the bruises on it, the way the shadows make it 3-dimensional. When you look at that banana, look past the banana and focus on the outside edges of the banana. How does the outside curve.
One practice that my teacher taught me that was super helpful was blind contour drawing exercises. This is where when you are drawing an image or environment, you are not allowed to look at your paper, and instead focus on drawing the outside as accurately as possible.
This exercise allows you to switch your brain from thinking of what the banana looks like in general and turn on your ability to look at pieces of the shape instead of the piece as a whole.
So if you are wanting to learn how to paint, this should be your first step. I say that because my favorite part of watercolor is using it to shade facial features, so no pencil shading is ever required!
By Pablo Picasso