Those with humility submit. Their dealings with other people are very restrained.
It is interesting that Peter says "be clothed with humility," which in Greek literally means "put on the apron of humility." An apron is a symbol of service. He is likely thinking back to the last Passover with Jesus, where He "took a towel and girded Himself." Then what did He do? He served. This leads to what humility produces next: The humble choose to serve. They do not fight—they serve. They do not judge—they serve.
The Bible shows quite a number of men who did not look humble on the outside but were in reality—in the eyes of God—humble! Moses and David were both warriors and powerful political figures. In what way were they humble? Regardless of what they were—judge, king, prophet—they submitted to God. Regardless of what it cost them, they submitted to God, and sometimes they had to give orders or do things that we would consider to be quite difficult to do, like going to war or executing transgressors.
For a person to be humble in the biblical sense, he must know what is true and right, have a good grasp of reality, and submit to it. Ephesians 5:21 and Philippians 2:3 both show in broad principle what humility tends to do to a person. He is restrained, but at the same time, he is constrained to serve and to submit. Conversely, those who destroy unity are those who exalt themselves against God, men, doctrines, and right traditions (II Thessalonians 2:15; 3:6).