Fitt's Law
The time required to move to a target area (e.g. click a button) is a function of the distance to the target and the size of the target. In other words, the bigger an object and the closer it is to us, the easier it is to use it.

GOOD

BAD
Hick's Law
Every additional choice increases the time required to make a decision

GOOD

BAD
Consistency

Elements or content that appear in various places on a website should be consistent. This helps keep the user familiar with the site, which makes it easier to use and understand.
Gestalt Design Laws
The human eye sees objects in their entirety before perceiving their individual parts. Also known as the unified whole.
Proximity

While they continue to be separate shapes, they are now perceived as one group.
Similarity

The symbol appears as a single unit because all of the shapes have similarity.
Continuation

The viewer’s eye will naturally follow a line or curve.
Closure

If enough of the shape is indicated, people perceive the whole by filling in the missing information.