The best exercise to go from drawing to painting in the most natural progression, is to paint mono-chromatic paintings, AKA monochromes, or paintings done in a single color. Really any color can be used, even yellow or gray, but it is best to use a color that can span more of the value scale, like blue, black, red, green, or I really like Burnt Sienna. There are two methods to these, the first more like drawing, the second, more like painting.
6a. Transparent Monochrome:
The first method is a transparent approach where the white of the canvas comes through the lean transparent application of the pigment. For the lighter values, wipe out the pigment, like erasing to let the canvas come through. Build up the pigment for darker values. This method is most like working in charcoal, but is not a lot like full-on full-color in the opaque medium that is oils.
6b. Opaque Monochrome:
For the second method, a more opaque approach is used to create value. White will be added to the color mixture to create the appropriate value, so once again, you’ll want to use a darker valued color for this. Ivory black is obvious, but any darker value will work including a gray mixture. This method is much more like the complete experience of oil painting