This guy has some nice vids out on how to play classes in TF2. He really seems to know the game and his videos have a lot of handy tips and strategies that help with general gameplay.
Watching these vids before I even played TF2 REAALLY helped me out a lot and I was able to actually do well with some classes right as I stepped into the action.
Some of the tips he has in here are actually very amazing and things I never EVER would have known or thought of. I recommend watching all of them unless you REALLY know the game's ins and outs. They'll definitely help on an everygame basis.
Some of his music choices can be strange. Have a custom soundtrack ready.
How to play the Spy.
How to play the Engineer.
How to play the Pyro.
How to play the Scout. Part 1.
How to play the Scout. Part 2
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Indestructible. Determination that is incorruptible.
Very nice videos. Spy one is incomplete (although I picked up a couple tricks from it), but the Scout vids helped me out the most. I didn't realize the pistol and bat were so effective. I'm mostly a jumpy, scattergun spamming blip on the screen.
Of course, now I can't get on TF2 to put it into action.
But they're still good and full of nice tips and strategies about how to combat a class with another class. And I'm sure not everyone has seen them so I believe it helped at least a few people out, which was the whole point anyways.
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Indestructible. Determination that is incorruptible.