Some in-depth knowledge on positions, formations, and tactics is available on Wikipedia. Please note that I haven't tried incorporating any of the information into my own game yet (I just ran across the articles today), so use any of the advice there at your own discretion.
These links are probably more useful for those with extensive FM players who are looking for an extra edge or like to experiment. I found some interesting tidbits on using free role with a sweeper and swapping positions when a playmaker is man marked.
Cheers.
http://en.wikipedia.org/wiki/Footbal...r%29_positions http://en.wikipedia.org/wiki/Formation_%28football%29 http://en.wikipedia.org/wiki/Footbal...ics_and_skills 
Tactical Knowledge for the Afficionados 
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