Building common ground is difficult and not natural for many of us. On the other hand, common ground is one of the essentials of living together in tight spaces (cities) and increasingly politics and professions. Often the building of patriotism makes building common ground nearly impossible. We can spin our wheels looking at all the problems that face us when we're trying to build common ground. Instead, let's look at what we can do individually to increase common ground.
1) Since one of the of easy and comfortable things we do everyday is travel with people who think like we do and in fact do many of the same things we do. We can deliberately set out to find, listen to and ask questions of people who are clearly different from us.
2) Since it is quicker and easier to take the same route to work or to visit friends every time, think of ways that can vary that path. That might expose us to a different set of challenges causing us to think differently about the world immediately around us. That may cause us to rethink some things we held to be true when we view new sets of data.
3) Since we have limited resources in general we tend to read, view and discuss things that are clearly of importance and value to us and our kind. Periodically set out to read things that you expect/know you will disagree with. Try to do it with an open mind. Go to a movie that others seem to enjoy and you know you will hate. To better understand, even if it is so that you can better handle folk who think a certain way, why people do what they do, carry on a discussion the goal of which is to better understand rather than to persuade.
Put another way . . . seek information, a perception check if you will, rather than trying to change their mind or make them feel inferior. After you have gathered the information think about it. It can be very rewarding and it may very well lead us to encourage the building of common ground.