The Pyro
The Pyro cannot be played like many other classes in the game, he is quite unique. He lacks the long-range firepower of the Sniper and the concussive force that powers the Soldier and Demoman. He's nothing even close to subtle and doesn't do well in many circumstances. However, when used properly, a Pyro in skilled hands can be the bane of any team, it is my hope to help get you closer to that point. But first, lets start with the basics:
Pyro Weapons
Flamethrower
Nothing is more deadly at close range than a Pyro's flamethrower, especially if that Pyro is critting. Press the nozzle of your flamer into any class, even when overhealed or still attached to a Medic, and within seconds they'll be charbroiled and waiting to respawn. The key to taking down big classes and Sentry Guns is circle strafing. Stay in one place and you'll get snuffed out quickly. Learn to keep moving yet still keep your reticle focused squarely on your target. The Flamer coems with plenty of ammo and unless you abuse the airblast feature, you should rarely have a problem running out of flames (especially since every enemy you kill and grab their gun gives you 100 more ammo).
To this end, don't be shy about puffing everyone who gets near you with a little burst of flame. You waste only a tiny fraction of your ammo, your teammates don't care, and you'll uncover Spies. Spy checking is one of the implied duties of the Pyro. Ignore it, and your team will soon remind you. Listen for Engis to call their machinery sapped and immediately douse the area in flames to keep the Engis safe and possibly uncover the Spy.
On the subject of airblasts, they're all a matter of timing. Normally if you come face to face with a Soldier, his first reaction will be to shoot a rocket. Counter this by the moment YOU see that Soldier, immediately airblast. You'll give yourself some breathing room from him and probably send his rocket back at him. From there, you can try to continue reflecting, or he'll pull his shotty, in which case, you've just gained the upper hand. Charge in and toast him. Pipes work similarly to rockets, though harder to reflect effectively. If a Demo is spamming in a consistent rhythm, watch a couple, dart in, throw one back at him and duck back out again. A crit reflected pipe kill is one of those things that you think of later that night after the game is over and smile
You can reflect stickies, though this is quite tricky as the only effective way to use them offensively is to blow them back into the Demos face and make him blow himself up. Most Demo's try not to stay that close to their stickybomb carpets, so this is only marginally useful. Blasting stickies is better used to clear them from your teams path in a more controlled way than rockets and stickies do. Finally, watch for players on perilous ledges (ex. Point E on CP_Steel) and send them flying to their deaths.Don't forget the value of your afterburn. If you're storming a fortified location, instead of aiming for individual players, light as many up as you can first. Not only will this guarantee damage to the team, but nothing sends people scattering like bursting into flames. You never know who might be hurt and just need that little bit of fire. Watch and listen for players calling for a Medic, they're usually quick cooking. Should your burning enemy withdraw beyond your flamethrower range, that's when you pull your...
Shotgun
The Pyro is not a long range class, but the shotgun is all he has out there to defend himself from anything beyond slightly-past melee range. It's best time to be used is when chasing down an enemy you've already burned. They may run to a medkit and heal, but even the small bits of damage you're doing with your shotgun add up and can get you the kill. Though far from reliable, you can mess up Sniper shots with your shotgun. It's useful to use for some damage while approaching a point where your primary can be used (i.e., storming the bridge on the start of Warpath. Peppering the enemy with buckshot before reaching them to ignite may not do a ton of damage, but some is better than none.)
Flare Gun
When using the Flare Gun, hit Esc, open the Pyro's Weapon Loadout, and switch back to the shotgun.
Fire Axe
Though I'm certainly biased towards it, no Pyro worthshould forget his axe. The Pyro is built to fight at close range, and melee is just a touch shorter range than his flamethrower and certainly makes for a stylish kill. Other Pyro's are often your best bet for axe attacks. As many Pyro's will simply flame whatever is before them, a melee Pyro can take surprisingly little damage with a little fancy footwork and leave the enemy wondering what just happened. It's best used in single encounters unless you're skilled with melee and even then, you're a pretty big target.
Axtinguisher
When using the Axtinguisher, bear in mind that you do next to no damage to people who are not burning, so dont go rushing in unless you know you're going to crit something. A good use of the Axtinguisher is to flame your enemy, airblast them up against a wall, and while they're dazed and tyring to regain their bearing, WHAM. It's a flashy looking move and deadly effective. Try to run with other Pyros, especially following an uber one and clean up the burning enemies he leaves in his wake. Most will be more focused on the uber that what follows and that is to your benefit.
Ubercharges
As a Pyro, you're a prime recipient of Ubers. Though not as effective as a Demo, you can eradicate Sentry nests fairly quickly. Simply focus on them and run straight toward them. Provided you have little intereference, you will reach the sentry, then it's just a matter of circle strafing it and killing the machines and their Engi. Once that's done, start rushing anyone alive. An uber Pyro sends a team fleeing like little else, so use this to your advantage. Carve a blazing path and your team can move forward. As a matter of personal preference, I consider Pyro Ubers to be one way trips. My Medics can flee, but I generally don't leave where I've ubered into in one piece. You're still feeding off that chaos and disarray you've sown, use it to send a few more points of damage against the enemy. Besides, if they're dealing with you, they're payign less attention to your teammates who should be moving up to support you.
Let me repeat for emphasis.
Follow Ubered Pyros. They will clear you a path like little else can and will allow you to move up quite a distance. Nothing irritates me more than a fantastic uber run, clearing a whole area to find my team still sitting back at their encampment twiddling their thumbs and aiming at the doors.
Class Strategies
Scout - If you get the jump on a Scout, you're already ahead of the game. Your afterburn alone will claim more than half of his health, so smart Scouts will generally avoid Pyros and flee from them if ignited. They will leave your flamethrower range quickly, so pull your shotgun and take them down before they get away. They're most effective at a range that you too are quite deadly in, so most Scouts will avoid a head-on Pyro assault.
Soldier - If you're using the original Flamethrower, try and send his rockets back. If you can, you'll likely frighten him into pulling his shotgun, which makes him easier to kill at flame range. If you're not good at reflects or using the Backburner, strafe like mad from his rockets and pepper him with shotgun blasts while you get in range. If the Soldier is aiming for your feet, consider retreating.
Pyro - Against other Pyros, the battle usually comes down to whoever manages to keep the other in their reticle for longer than the other. You suffer no afterburn from them, so don't be afraid to take a little damage. Shotgun blasts and the fire axe are excellent options against a Pyro expecting flames.
Demoman - Demomen aren't hard to kill, they're just hard to approach. Watch for the Demo's stickies and blow them away if they get in your path. Try and reflect his pipes if you can, but it's tricky. Once you're in flamethrower range, all he has is his bottle to fight you without hurting himself, so unless he manages a lucky crit, you're going to win this one.
Heavy - Heavies are dangerous only if they see you first. If they know you're coming and spin up and fire appropriately, you've got no chance. If you can sneak up behind a Heavy, especially one with his Minigun not revved, you stand a good chance of taking him down. Remember to circle strafe.
Engineer - All by themselves, Engis are a piece of cake. Fire, shotgun, axe, they're pretty vulnerable to all. The Engineer isn't the problem though, it's the toys that he is invariably surrounded with. Some Sentries just aren't reachable, let alone destroyable, by an unubered Pyro. Leave those to the Soldier and Demos. If you can get the jump on a sentry around a corner though, and stay moving, you'd be amazed how quickly even a LVL3 can go down. If you're lucky, you'll take out the Engi too.
Sniper - The Sniper is the polar opposite of the Pyro. He excels greatly at long range but falls rather short on the close range. So, if you're far from him, he will kill you, if you are close to him, you will kill him. Crits aside. If the Sniper is taking aim at you from his nest, spray him with shotgun blasts to try and throw off his shot.
Medic - Medics are easy prey. If you see one, always go for him. He's a prime target and has little to defend himself with. Just watch for his teammates. Even the most selfish of players will be hard pressed to ignore a Medic under attack.
Spy - If you find a Spy in your range, he's yours. Unless he crits or picks up a medkit and stealthily cloaks away, there is little to save a Spy once a Pyro has seen him.
Bear in mind with all classes that you deal your damage in a range very close to the enemy, where most shots do the most damage. Remain aware of what is around you and who is aiming for you and make a tactical retreat if necessary. Also, you're a prime target for melee attacks. Players backed into a wall with no discourse may make a mad swipe with their melee and get a lucky crit. It happens a lot.
To be continued...
flare gun. The hit detection on flares is really generous, if you get it in their general area, they will light up. As for using it in conjunction with the axtinguisher, I would have to disagree, those 2 weapons actually work very poorly together, the only reason you would use the flare is for distance, and the only time you can use the axe is close range. That is not to say I don't use both, I just don't use the flaregun with the intent of hitting someone with my axe.
Looks really nice 
... but shame that i dont like pyros 
