-The special grenades he carries last long and are a pain to the other team.

-The pyro is somewhat fast, too, so maybe a flag cap here and there would be nice.

-Throw your secondary grenade in a doorway or at a choke point to slow everyone down.

-Throw your secondary grenades, shoot your flamethrower, or shoot your incendary (?) cannon at snipers to catch them on fire. They can't snipe while burning!

-Assemble an attack team of a scout, a pyro (you), and a HW guy. While the HW guy is chopping through the enemy, you're circling around them with your flamethrower bursting and the scout is sneaking through all the action to grab the flag.