Bookmark network casting websites and check them every week. The network casting calls will include casting details about current shows as well as any planned shows. A viewer may find a proposed show is more appealing than anything currently on the air.
Watch websites that gather multiple casting call announcements into one place, such as realitywanted.com. While these sites are not always current, they can provide valid information about where and how to get applications.
Sign with a casting agency or talent scout that specializes in reality television shows. An agent will submit head shots and details to casting agents looking for your "type." Some reality shows that don't do casting calls do look for contestants through these normal talent channels.