There lot of options one of them SUPER CANCEL
the keeper go down and u shoooot and SCOOORE
also in PES 2012 u have many skills like Rainbow Fliking, Elastico, Cross OVer Turn , etc ..
so easily u can score but I use SUPER CANCEL (Hold Rectangle _when the meter fills_ Press X button then shoot with rectangle)
the best way but make sure there a distance between the ball holder and the keeper