Sometimes I get asked for a couple of pyro tips, and well it's kinder hard to really explain them all in chat so here's a post I'll refer people to and hopfully people will find it helpful if they play, or are looking to play pyro. I will add more to this thread as I go if people like it, so far I've covered simple plain old flaming. Feel free anyone to do your own class write up thread. SpA members or not, just make sure you know what you're talking about The Flamethrower
Flaming is the most basic and the most important aspect of pyro, and it is usually ignored. Now there's a great deal more to flaming than w+m1. The flamethrower shoots particles to register it's hits and is poorly represented by the flame effect that you see on your screen, the best thing to do is turn your hit sounds on to get a better idea of how your flames actually behave. The best way to imagine particle behavior is to imagine you're firing a hose so if a targets moving to the right of you don't just aim your flamethrower directly on them, aim the flamer slightly before the direction they're going in so they walk into the particles which have more time to travel the distance. Particles also decay, that's why you do more damage up close. This is a great way to defeat enemy pyros, if they w+m1 you, all you need to do is s+m1 them by running backwards flaming so they are running into your fresh particles while you take minimal damage from their decaying ones.
Also remember when attacking enemies you can strafe and around them, while still flaming. This confuses them and makes it harder for them to hit or find you (this also works on sentrys if you do it right). The flamethrowers can also penetrate though enemies to damage others. Now the particles have hang time, and there's some neat tricks you can do with this, like flaming as you run backwards round a corner, you are essentially laying the particles as tiny traps to whoever's chasing you. If there's a gap between you and an enemy you can run until you hit the gap while flaming, the particles inherit your momentum and will go further than if you weren't moving.
The flamethower defines the pyro, you have to know how it works and how to exploit it. Using your other weapons and airblasting is of course really important but are complimented by milking as much damage from your flamethrower as possible.