There are several ways to enhance your skills.
The Michgian Referee Committe provides instruction at certification and re-certification classes. USSF also offers videos, position papers, interpretations, and an ask-the-ref section. Go to www.ussoccer.com, and go to the "referee" link on the left. Additionally, the Grand Valley Soccer Officals Association (GVSOA) will offer a pre-season "tune-up" or class. The goal is to review and reinforce knowledge and skills prior to the season, and to update the referees on any changes/modifications by USSF during the off-season.
The GVSOA has many different levels of resources to assist referees in developing their game and management skills with the ultimate goal of assisting them move to higher referee grades.