In order to receive a varsity letter you have to meet some simple criteria. First and foremost, you must put in 10 hours of volunteer time. Do this for the schools, the community, your church, your neighbors, etc. It does not matter what you choose to do, but please have an adult sign off on your hours worked.
Second you have to be a competitive member of the team. This number fluctuates based on the number of girls on the team, but typically you need to consistently finish in the top 2/3rd of the team.