It’s easy to get caught up in the one thing you’re testing right now. This narrow view of the world (or system) makes it easy to miss obvious problems.
One technique I use is to always scroll to the bottom of the page. It doesn’t matter if my test calls for me to click a link in the page’s top nav, first I scroll down, then I click my link.
It takes just seconds to scroll to the bottom of the page. By taking just a little time to broaden your view of the world you might find you see some surprising things.