The team I play best with in PES6 is Barca. Im undefeated. I use short simple passes and knock the ball around and play possesion football, Its Barca so they are already skilled at doing so, but it works very, very well.
Like when kicking off, I always pass the ball back to Gio and look at the radar to see who has space, it does help other players to make spaces aswell and when I get a goal kick, I short pass it to the defender whos closest to me, intead of knockin it up field to lose it in a header (Because Barca arent the biggest team) and then I work it from the back and having three pacey frontmen in Messi, Eto'o and Ronaldinho its usefull to get the ball to either of those three and if need be, you try and make a run, if you lose the ball youll have about 7 other men behind it so you have a good chance of recovery, aslong as you dont dive into a tackle and be patient.
The best thing that I do is play simple passes all about the pitch, which draws my opponents out to me, I never panic and clear the ball in my own box, I play my way out because theres always someone outside the box who can collect it and move on. So always use your radar.
EDIT: Its ok to do some tricks now and then, mainly the one that lets your player let the ball shift past him which gives you a good advantage and slow dribble is usefull too, in tight areas