Via kottke.org, Jenna Fischer explains her way of success in TV comedy (and plugs NBC’s The Office, gently):
So, how did I get The Office? … I developed a relationship with [Allison Jones, casting director] — not because I met her at a party and we “schmoozed,” but because I had proven to her over the course of many years that I was a reliable and serious actor capable of providing a consistent body of work.
Works that way in the amateur ranks, too.