The way I was taught was to use the "old masters' method. This typically means that the base painting will look similar to the one above. You start with the basics, only a monochrome base and the basic shapes and forms of your subject. As you can see, even though only one color is used, the painting still has depth and form. The great thing about oil is
layer after layer of paint can cover up mistakes and change the painting as you go along.
The next step is to add the local color. This can be done by with regular painting, washes, glazes, using a palette knife or many other options. Adding the color allows you to see how the objects will look in relation to each other and the background. Ideally, the colors should be complimentary. As more and more layers of color are added, the painting will look richer and more vibrant. There are many options for paint brand, color, and medium that are added to the paint and all will give the painting a different effect. There's so much more I still have to learn about using the right paints and mediums.
The last step is to varnish the painting if desired. This will keep the paint safe from moisture and dust. Unfortunately you have to wait until the paint is dry before varnishing and this can take up to 6 months to a year! Again there are many different types of varnish from glossy to matte, Damar varnish to beeswax varnish. So many choices! Familiarizing myself with all the different options will take time, but I find my paintings are getting better and better as I discover new materials and techniques.