The six principles of landscape design are balance, proportion, unity, rhythm, emphasis, and simplicity. Balance is the visual weight on each side of a view, either symmetrical for a formal look or asymmetrical for a natural one. Proportion keeps elements sized to the house and to people; a 10-foot pergola overwhelms a small patio. Unity means repeating materials and plant shapes so the yard reads as one design.
Rhythm comes from repetition, like the same ornamental grass every few feet along a path, which pulls the eye through the space. Emphasis gives the eye somewhere to land first, such as a specimen tree or a fire pit. Simplicity is restraint: fewer plant varieties in larger groups beat one of everything.
The fastest way to learn these is to see them applied to your own yard, which is what AI landscape design generates from one photo.