I've been playing a lot of pubs for a long time. What steps should I take if I want to give competitive TF2 a shot?
You can freely join leagues (like the UGC) to get yourself noticed. You may also be able to network with other players and build your own team.
Another option is to pug for competitive teams. Idle on IRC (like gamesurge) and offer your services.
One source I found was TF2Center. This will automatically set you up into a pick-up-group, so you don't have to manually organize one over IRC.