Learning to paint well takes years of practice. You may have visited a museum and been totally amazed by the works of a particular painter. Just remember that paintings, even those of great artists, aren't created by magic. All great painters have a method. Something I've done that has helped me learn about painting methods is to study the unfinished works of master painters. Here are some images from Wikimedia Commons Image Database. First is a painting of Anders Zorn by the Swedish artist Bruno Liljefors.
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As you can see Liljefors started on a toned ground (possibly a mix of Naples yellow, white and a little black).
Although the head is fully rendered you can still see that the painting was started very simply using loose areas of color painted in without any real underdrawing. This is a form of what is known as 'direct painting' which means that it is worked up from the beginning using full color to establish the shapes and values. Notice the red reflection on the jawline and how a band of cool background color is used along the head just before the light areas turn towards the shadow side.
Next is a painting by Thomas Gainsborough. In his painting the canvas is tinted with a darker umber or sienna and an under drawing is sketched in using this brown along with black. Even the face is only rendered by the addition of white. A monochrome underpainting of this sort is used to work out the values and composition first, leaving the other more intense colors to be added later .
Study the unfinished works of other painters and see what you can learn about their technique.
The more you learn about different techniques the more you will be able to understand and develop your own style.
