How did you boost your self-esteem?

As hard as it sounds to say this, but whenever there's another guy who looks stronger, taller or more good-looking than me, I can't help but feel like I wouldn't even be able to start up a conversation. I feel dimished and can't help but compare myself to the other dude. It seem like we are both in completely other levels. The thing is, I work out every day, take care of myself and am not socially awkward. Despite all of this, I can't help but feel that others are "better" than me. How do I break this cycle of insecurity and build up my self esteem?