I'f you looking to go commercial be very strict with yourself. Plan your nav's in great detail dont except any height / heading deviation throw in the odd diversion. Stall current on Stalls' PFL's EFATO's etc. Dont use a gps (maybe as backup).
The above advice is what I was told when I started my hour building. I'm starting CPL lessons tomorow and starting to wish I had paid a bit more attention to it :-s