Team Fortress tips

Demoman

Use sticky bombs and grenades to guard areas and take out enemy sentries.

Strategy Your bombs can reach where straight-shooting characters cannot, use this to blow up stuff around corners, through windows and over ledges while remaining out of the line of fire. Use sticky bombs to protect an area, even ones you can't see, but which have a vocal trigger when activated - ie: "The Control Point is being captured". In a one-on-one battle, try to land your grenades on the other player, or drop sticky bombs and activate them when they run over them. Alternatively, use the shotgun.

Strategy vs. Anyone with line-of-sight to them is the demoman's worst enemy, as you can dodge their bombs and distract them from what they were doing. Heavies, snipers and soldiers are particularly effective.

Engineer

Build objects to defend, transport and resupply your team.

Strategy Build turrets in hard-to-see places, when viewed from the entrances. Think how the other players aim and check all the angles to see whether they can get a shot in. Build dispensers near your turrets and teleporters when maps are large. In sudden death, build a dispenser. Using dispenser to block paths is a cheap trick not worthy of you. Stay next to your turret with spanner equipped to defend it from spies and repair it. Smack anyone who comes near with the spanner.

Strategy vs. The spy is the engineer's worst enemy, with the ability to sneak past and sap their turrets. Demoman can reach turrets others cannot, and heavies, snipers and soldiers can take them out at range if given line-of-sight.

Heavy

Shoot lots of bullets in the general direction of the enemy team.

Strategy Get your weapon spinning before going around the corner to known enemy activity. Don't take on a L3 sentry without a medic. Don't try to chase anyone, decide where you're going to defend/attack and keep on that path.

Strategy vs. The scout is the heavy's worst enemy, as not only are they too quick to hit, but they've got couple of nice weapons to rough them up with from behind. Generally heavies are best avoided unless you're a heavy with a medic yourself.

Medic

Heal your team for kill assists and an invulnerability bonus.

Strategy Heal constantly, selecting charcters in order of most armour downwards, so your beneficiary is likely to last the longest. Keep out of sight yourself, but don't let your charge get too far away. Make sure your partner is ready and has enough ammo before activating the ubercharge. Try not to ignore calls for you help, unless it's someone who has cried "wolf" too many times.

Strategy vs. Pyros are an enemy of medics, as their flames can only be extinguished by medics (or water). Otherwise aim for the medic who's healing another character to avoid having to kill the other character twice over or more, although bear in mind the medic self-heals over time.

Pyro

Light stuff on fire and watch it burn.

Strategy Light a bunch of enemies on fire to cause panic and get engineers to flee from tending their sentries. Torch snipers to ruin their aim, wave your thrower with impunity amongst your teammates to check for spies. Not the most effective, but one of the most fun to play.

Strategy vs. Run away. Really simple, they can't do anything with the flamethrower when running forwards. So, worst enemies are anyone at least as fast as them and medics for extinguishing their flames.

Scout

Run and capture stuff, you count as two people on some control point maps.

Strategy Keep moving and hardly anyone will be able to track you, use your ears to listen for sentries, and eyes to look for sticky bombs. Try and trick demomen into premature detonations by double-jumping over their sticky bombs.

Strategy vs. A well-positioned heavy or engineer's sentry is the worst enemy of the scout, as they can do nothing until reinforcements arrive. Fun to watch them try, though.

Sniper

Take out enemies unseen at distance, destroy turrets where only the corner of them is visible.

Strategy Stay zoomed and focus on an area for maximum damage, but don't let your glowing dot be seen. Change your position every few kills to confuse the enemy - particularly now the killcam reveals your position. Try and find unexpected places to snipe from, rather than the obvious. Running to the spawn room is often a better idea than trying to use the useless auto-sniper. Creep around corners to kill turrets without them spotting you.

Strategy vs. Worst enemies are other snipers, but spies and pyros can help to make their lives a misery. Rocket-jumping soldiers can quickly turn a safe sniper's nest into a bloodbath, too.

Soldier

Shoot rockets and blow stuff up.

Strategy Shoot at the floor and try to time it correctly. Even bunnyhopping losers have to land sometime. Pop around corners and fire off rockets to take out guards and sentries without taking too much damage. Reload ahead of time.

Strategy vs. Either stay far enough away to dodge rockets, or get so close they're scared to use them. Jumpy scouts are the soldier's worst enemy, along with engineers who place turrets just around tight corners they can't shoot or dodge around without taking a lot of damage.

Spy

Sneak invisibly or in disguise into the enemy base, then sap their turrets and backstab them.

Strategy Don't be obvious. Cloak and disguise when out of sight, don't let them see you coming out of your own base in your disguise. Don't make a beeline for turrets. Try not approach the person whose class you are disguised as, as it'll likely show their name on you. Don't sap machines with the owner standing next to them. To backstab you need to be disguised or cloaked, but most importantly, attacking from behind. Keep the cloak for when you need it, and try an make an unpredictable movement once using it, getting to an out-of-sight place, letting it recharge and the enemy to have forgotten about you.

Strategy vs. Worst enemies are pyros and engineers. Pyros because they can flame their own team to weed out spies and engineers because they know when their machines are being sapped. Anyone who's observant can detect them, though - watch for suspicious behaviour, inability to enter the spawn room, duplicate names, speed not consistent with the character (ie: fast heavy) and general lurking , skulking and plotting. Don't shoot spies your own colour or which say "disguised as..." on them, it may be a scary experience seeing a spy, but they're actually on the same side as you.