Do not actively try to become a Sidekick or True Love. If you really have what it takes, you'll wind up with the role no matter what you do. Sometimes, you will be drawn into some new role or destiny by default, be it hero or villain. If the character was always intended to be important, that's a Chekhov's Gunman. If the character was hiding their identity during their first appearance, you have a Red Herring Shirt. If a character in an adaptation is introduced earlier than in the source work, that's an Early-Bird Cameo.