Just sign into Xanga, and visit the blogring you'd like to make sure to avoid leading.

See on the upper left, where it says:

Members:
» Invite Members
» Approve Members
» Manage Members
» Your Membership

Just click on "Your Membership", and then on "Opt-out of Moderation". 

You'll be asked to signin, and then to confirm that you really want to edit your settings.  This confirmation helps maintain your site security.

Once you arrive on the Opt-out page, there should be a line which says:

Leader:  Would you accept leader status?

The default setting is to accept leader status if offered.  If you'd like to make sure that you can *never* become the leader of a blogring, tha change the setting to "No" and click on "Save Changes"