These tips will help you select well-composed images and crop your selected images successfully:
The “rule of thirds” helps you find where the points of interest in an image should be. Divide the photo into thirds both vertically and horizontally—points of interest appear at the intersecting points rather than in the middle of the frame. The first photo here is cropped without using the rule of thirds, the second is cropped using the rule of thirds. (Attribution: https://commons.wikimedia.org/wiki/File:RuleOfThirds-SideBySide.gif)
Symmetry is what makes a photo feel balanced and calm. If you divide the image in half down the middle (vertical or horizontal) is there balance? Something slightly off-centered can feel extremely unbalanced. This doesn’t mean the subject matter has to be cut directly in half in the middle and be equal on each side (although it can), but just that the weight of the image as a whole feels centered.
Uncluttered backgrounds keep focus on the main image and make a photo easier to read.
Sometimes a simple change can make a big difference. The first photo here has the subject centered and a distracting background. By cropping the photo, you get a tighter focus on the subject, a more interesting layout, and a less distracting background.