Basically, the overall structure of the team is the most important thing, even if it means sacrificing the odd players skills, for instance if a DM has high dribbling they still should not make forward runs.
Speaking of DMs, in my opnion, you always, always need one. I've experimented with lots of tactics and I've had to put a DM in every one almost in order to concede less goals. A MC who never makes forward runs and play defensively is good (ala Fletcher) but I highly recommend a pure DM (ala Hargreaves).
Also, you need to make sure that your 2 strikers, or your striker and AM or whatever combo you have, have the right balance between them. Generally one should always be in a more reserved role than the other, and play further back, basically acting as the connection between the midfield and the frontline, and be able to hold up the ball.
The best thing the guide does is split players into 3 groups, defensive, support and attack. DCs will always be defensive, that is never make forward runs, cross rarely, no long shots, no run with ball etc. In my opinion, you always need one midfield who plays defensive (the DM) and one who plays as support (a CM). A support player is, as you probly guessed a mixture of attack and defense, they make a few forward runs but they're not too creative and they'll still track back and defend. You should always have one of your strikers as support (the 'connector'). Your other striker should then always be attack (lots of forward runs, through balls, creativity etc).
On the wing is where things vary, if you want to play atacking, set your wingers and full backs to attack minded, if you want to play standard/conservative, set full backs to support, and if you want to play really defensive, set full backs to defensive (for overboard defense you could set wingers to support, but your attack would be numbed)
Anyway, that's just the jist of what I learned, there's feckloads in the pdf, it took me a long, long time to read.
