A big thing people do is over rotate your chest and pecs.
You only really have to do it minimally just so that you don't fall over because you also have to anticipate how that arm movement will affect your next step and then you also have to think about how you're going to adjust for that.
The entire chest area is really one of the most key factors in running. You generally want to keep it as straight as you can when running to prevent loss of balance.