Mrrrf- urffff mfmmfrm!
The pyro has recently been substantially upgraded by Valve, giving them three new amazing weapons - the backburner flamethrower, the flare gun and the axtinguisher. These three have combined to help make the pyro even more fearsome than he was before, and the numerous achievements released in the update pack has made it one of the most popular classes currently. The pyro is most effective when deployed in a close quarters indoor map with plenty of choke points. The flame thrower is nearly ineffective when deployed against other pyros, but will make quick work of any other class if they get the jump on them. Few people can use the flare gun effectively, but it and the shotgun provide quality medium to long range attacks for when someone runs out of range.
One pyro will have a very difficult time burning down another one, so it only really makes sense to use the class when a third or less of the opposite team is made up of pyros - no matter how hard you want to work on your achievements. You should use your superior speed and low profile to try to hug as many walls as possible. Your ideal situation is to pop out from either behind your enemies or around a corner, so that you can kill them before they can react. Pyros are also particularly good at frying medics easily. One common and effective tactic is to charge recklessly towards a medic to burn him, stopping the opposing team’s advance and likely getting killed in the process. If you don’t mind that, it’s a great way to help your team out.
What separates merely good pyros from great ones is the ability to decide when to disengage from a fight so that you can live to roast anothre person. Keep in mind that you don’t need to burn someone all the way in order to kill them. Sometimes, you just have to light someone on fire to send them running back into their own lines. Unless you’re playing purely to see your own score increase, the ultimate objective is to push the other team back so that you can take their objectives. Just setting someone on fire will generally freak them out and cause them to run for a health pack or medic - and that’s time that they’re spending not shooting at your teammates or pushing on offense. Get kills, but also stay alive as long as you possibly can - the less time that you spend running back from your spawn point, the more people that you’re going to be able to turn into crunchy bacon.