Cropping is how your image is framed (what part of the photo you can see).
Alignment is how the different elements in your design line up with each other.
Proximity is the sense of distance between objects.
There are many other things a designer has to consider.
Balance - symmetrical or a-symmetrical
Symmetry - elements on both sides are arranged similarly
A-Symmetrical - elements on each side are different but still visually balanced
Hierarchy - the arrangement of elements in order of importance. For example, different weights applied to show hierarchy.
Scale/Proportion - elements of differing sizes in relationship with each other
Similarity and Contrast - Contrast with a clear foreground and background shows a focal point.