Gotfrag has a large selection of demos online of (mostly) cevo-matchplay. You can learn a great deal watching those pro-players play the game.
The main advantage of watching a demo over watching a vid is the relative small download and full-screen vieuwing (as you are watching them on your own copy of tf2)
Just download a couple of the top-downloaded demo's, extract the .dem file in your C:\Program Files\Steam\steamapps\*user name*\team fortress 2\tf folder. Fire up tf2 and press shift-f2 to bring up the playbacktools and use them to select the .dem file and play it (alternatively you can type 'play *demoname*.dem in the console).
Have fun!
