This question has come up quite a bit in the last week so I thought I'd add a tip to the blog.
If you're getting your site ready for the new season or are just starting out, you're usually the coach or manager and want to get yourself added to the Roster. Many admins try to add themselves as a new member. If you do that you will receive a message that you're already a member of the site. Instead, in the Roster folder use the Roster Pool to locate your name and assign yourself. Be sure you select the Type as "coach" when you assign yourself, unless of course you're a player. If you don't see your name immediately, select the appropriate Person Types then click "search pool".