Similarity and contrast, connection and separation, grouped and ungrouped are all ways to describe the varying sameness and difference between elements. Based on the information they carry, we’ll want some elements to look similar, to indicate that they are related in some way. We’ll also want to show that some elements are different and belong to different groups.
Key to showing both is the visual characteristics of elements and their relationships. If two elements are related in some way, then they should show similar visual characteristics. If the elements are different, then they should look different.
http://www.smashingmagazine.com/2014/09/22/design-principles-connecting-and-separating-elements-through-contrast-and-similarity/
http://www.smashingmagazine.com/2014/09/22/design-principles-connecting-and-separating-elements-through-contrast-and-similarity/
