Rule of thirds
Split the frame into a 3x3 grid and put the subject on a line or intersection instead of dead center.
See it
What it is
Divide the frame with two vertical and two horizontal lines into nine equal boxes, then park the important stuff on a line or on one of the four intersections instead of dead center. The idea goes back to John Thomas Smith's 1797 painting treatise and survives today as the grid overlay in every phone camera app.
In practice it is three habits: put the horizon on the upper or lower third rather than slicing the frame in half, put a portrait subject's eyes near the top third line, and let the subject sit on a vertical third so the opposite side opens up as negative space. The off-center placement reads as considered rather than snapshot.
Gotcha: it is a default, not a law. Dead-center symmetry is a strong deliberate choice (Kubrick's one-point corridors, Wes Anderson's flat tableaux), and the golden triangle or a simple diagonal often beats thirds for dynamic scenes. Also, no grid rescues a boring subject: thirds decides where the interest goes, not whether there is any.
Ask AI for it
Compose against an invisible 3x3 thirds grid: place the subject on the left vertical third line with the eyes on the upper horizontal third, and set the horizon on the lower third so the sky fills the top two thirds. Leave the right third open and uncluttered, and do not center the subject. Do not render any grid lines, guides, or overlays in the image itself; the grid is a placement rule, not a graphic element.