The creation of abstract art can be a conscious or unconscious movement. Many times artists which start out with a blank canvas and many times have no preconceived idea as to what images will be there.
I would suppose the first act will be just to put some color on the canvas. It does not make much difference as to the actual color, but the starting color can trigger other thoughts of compatible or colors which break all of the rules. I myself like to have a color chart close by for reference.
The first motions need to be a sweeping, flowing motion. Just the act of this sweeping curvilinear motion actually might be setting the stage for the flow of the final image. With this sweeping flowing motion, it will set the stage for some smaller short strokes with different colors. Perhaps a dry brush or just a pallet knife will be used. Of course most any tool will become an extension of your thoughts when used in your hands.
Also the drawing of specific shapes just might trigger the use of a transition shape that you feel at the time should be added. If you think how squares and circles can be made into other complete images on their own, but can also add to the overall painting.
Of course abstract art can be in most medium, but some mediums are easier than others. I watched watercolor artists do an abstract painting while the paper was very wet. But when the blowers and places were covered up on the paper to dry slowly (so it could still be worked with a sharp object) the result was rather interesting.
As you are creating the painting you have to keep looking for the main element that you want the viewer to see. Will it be a dark area, light area, off to one side or right in the middle? Of course the rule of thirds (an image should be imagined as divided into nine equal parts by two equally spaced horizontal lines and two equally spaced vertical lines, and that important compositional elements should be placed along these lines or their intersections) can be a guide for you.
Of course some of the art you will be creating will actually reflect some of the other elements that you have seen other artists do, but will have you own unique way of doing them. You can also put lights in dark areas and darks in light areas.