There are many strategies you can use to help compose your drawings and/or paintings. One of the methods most frequently used by artists is the grid method; i.e., "The Fog Warning" by Winslow Homer (below).
When composing his composition for this piece, Homer used horizontal and vertical lines to divide the picture plane into thirds. (see example below)
In The Fog Warning (as in other great paintings), Homer uses the grid to control the viewer's attention, direct eye-flow and create a sense of pictorial order and balance. How the grid does these things, has to do with the way the mind's-eye works. Notice, that four intersecting points result from the crossing grid-lines. Intersecting lines create tension. Tension of any kind (whether actual or implied), attracts visual attention. Therefore, tension points can be natural eye-catching locations. This can be good or it can be bad, relative to how the grid and its "tension points" are used. He places the fisherman directly on the grid's upper left tension point. He places the schooner in very close proximity to the upper right tension point. These are the only pictorial elements whose placement so closely coincides with a tension point. Because they are placed at these critical tension points, the viewer's eye will automatically be drawn to them. Therefore, they must be key elements...and indeed they are. The fisherman raises his head to peer from under his hat brim, searching the horizon for the schooner that awaits in the distance. Angry clouds repeat the powerful diagonal of the boat and reach down towards the schooner in the distance. The fish in the boat stretches across the middle portion of a horizontal grid-line, it's swishing tail arcs towards the right tension point, leading the viewer's eye to the schooner. Choppy waves and white caps add to the drama. Homer's talent is formidable, but its the way he uses the undrlying regularity of the grid, that ultimately makes "The Fog Warning", such a masterful composition.
The mind seeks out order, balance and patterns in everything viewed. The compositional grid helps satisfy that search.
Notice, how Homer places the horizon in close proximity to the top horizontal line of the grid. This placement suggests to the viewer's mind, that the picture plane may be divided into horizontal thirds. Logic dictates that if the picture plane is divided into horizontal thirds, then it may be divided into vertical thirds also. Therefore, the mind begins to look for an implied grid pattern of thirds.
The mind isn't disappointed. Order prevails and a grid pattern of thirds slowly unveils itself.