One of the most often violated principles of visual design is, ironically, also its simplest — the principle of proximity:
Put things that are related close together, and space things that need to be seen as separate
One of the more extreme and frustrating examples of this can be found on the online banking site for ABSA (a South African bank):
The problem here is that if I select a beneficiary from the list I have to click the “Next” button that is at the bottom of the screen — far removed from the action I took in the dropdown. Instead, the “Add new” button, used to create a brand new beneficiary, is in close proximity to the dropdown, and therefore gives the sense that the dropdown and the “Add new” buttons are grouped together. The solution to this problem is so incredibly simple: just switch the buttons around.
Another example I came across recently lives in Outlook for Mac 2011. Let me first say that as much as I’m not a fan of Microsoft, Outlook for Mac is still so much better than any version of Entourage, so for that I am eternally grateful. But the implementation of email search really needs some work.