CVG just released their own key steps on "How to PWN in Team Fortress 2". They give 12 tips that may, or may not, help your game out. Some of them seem to rather tongue in cheek (the tips about being an admin being one example), but you never know what you might pick up from this list.
08. A real bindYou can read the rest over at CVG.
If you play a lot of Heavy or Medic, you'll quickly develop a case of Gamer's Finger. Holding that damn button down gets tiring. Configure your fire button to toggle instead. The code above says that if you're holding Shift when you click, you want to toggle your gun to fire constantly until you click again. You can let go of Shift, and clicking once after that will also turn auto-fire off. You could equally replace "attack" with "attack2" to make alternate fire toggleable.