How can one rid himself of excessive swearing and oath-taking, and what is the expiation for unfulfilled oaths?

To reduce taking oaths, remember the greatness of the Lord and that His name should only be mentioned in a befitting manner, as Ayyub (peace be upon him) used to do. He disliked mentioning God's name except for a just cause and would expiate for those disputing parties who mentioned God in their arguments. Also, increase in supplication and seeking refuge in God.