The Gestalt laws are pretty common vernacular in UI design. I thought I would review them a little for future reference. So here’s a handful of the more common ones:

• Law of Pragnanz — Reality is organized or reduced to the simplest form possible.

  

• Law of Closure — Objects grouped together are seen as a whole.

  

• Law of Similarity — Items that are similar tend to be grouped together.

  

• Law of Proximity — Objects near each other tend to be grouped together.

  

• Law of Continuity — Lines are seen as following the smoothest path.

  

And here’s other good links on the subject.