Market your quirks instead of trying to be the next big thing or look like the next Brad Pitt or Angelina Jolie. Some actors are not made for lead roles and sexy leads. If you happen to be one of those, then play up what makes you stand out from the gaggle of Brad Pitt wanna-bes and be weird and different.
Find your niche in stage shows, commercials and films. Just like Steve Buscemi, who was never up for the next action hero, you must find a group of characters that you can play really well. Whether it is the wicked stepsister types, the villains or the quirky side kicks, you can find the perfect place for your face and talents in acting and be a great character actor.
Broaden your repertoire. If you have your sights set on being a character actor, you should beef up your resume with talents and specialties that you see cropping up on stage and screen. Learn how to play the guitar so you can be the sensitive pony-tail guy, or learn how to handle a gun to be part of the next big mob crew on screen.
Hone your skills. Once you have found your place as a character actor, you need to continually work on your craft. Even if you aren't after the lead roles in every play or movie, you still have to be very good at what you do.
Try new things, and talk to directors and agents about what they think you would be good at. If you can't find your area of expertise on your own, these people in the business are your best resource for guidance and help.