The biggest mistake that almost all new players do is that they play way too many hands. An important skill that you must learn is that you should pick and choose which hands you keep and if it's pre-flop, this would not cost you any money. Patience counts a lot and the beginners will be too impatient and will force average hands, believing they have a winning hands, instead of actually waiting for those great hands to actually come.
Also, many players just fall in love with their great pre-flop hands: they would not fold even if the flop is disastrous. You need to remember that even the pocket aces can be beaten, too.
