I will probably play offline ML/tournaments/training and unranked games before diving into MLO, not that I'm a win% whore, I just don't want to completely embarrass myself!
I've begun scoring quite a lot of goals now on the demo compared to when I started, but still feel like I will get owned online

I know practically all sports games have cheap tactics that are unrealistic and overly effective, but I just hope that, on the whole, playing proper football will at least put you at near the same level as the people who use these methods (i.e. the PES4/6 cutback, the PES5 free kick bug, PES6 Adriano)...
On FIFA (even on manual) multiplayer games just come down to your gaming reactions and instincts, your ability to exploit the flaws in the game and use the same routes to goal. It does not make you think like a footballer, and if you force yourself to do so, then you will be at a massive disadvantage - admittedly, it has it's moments of genius, especially on Clubs, but generally, it's a joke of a game online (and just plain boring offline).
Oh, and one thing I like about PES 2011 (demo) is how you can use super cancel for defending/tackling again.
I kind of mastered this on PES5 (especially offline, lag made it more difficult online), and got so good at it that my friends "banned" me from using it against them

.
It's not quite as extreme as this in PES 2011, but here's 3 examples of what I mean from PES5;
YouTube - SuperCancel Defending PES5
They seemed to have removed that from PES6, instead of colliding, players slid past each other like they were covered in oil

.