Adding Default Role During User Creation

Hi,
How do I add user's default role when she/he is running Create User Wizard? I used the following statement but doesn't work. What event should I put the code at? I saw a video that did it by adding additional Wizard Step to allow the user to pick up his/her role. I don't want this additional step. I just want the default role to be hardcoded.

Roles.AddUserToRole(User.Identity.Name, "Visitor")Thanks,
Garreth
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