Learning to plaster takes some time, getting fast takes years.
not if you learnt from the right person,who was capable of doing decent meterage with a quality finnish.Once you can plaster to a decent finnish then its time to work on the speed /meterage .
Andy touched on it above when he mentioned being organised.This is one of the main ingrediants to being faster,having enough clean water there ready,plaster there ready,mixer cleaned ready,wash water clean ready,spot clear,walls pva'd ready,not sh i t in ur way.if you get a few mins inbetween trowels clear up or pva some walls or cut a few beads,a plasterer only stops for a (german word) a fag and lunch!!!
ive had people work for me in the past that have had there lunch break then pva walls after lunch and sit around waiting for 20 minutes " so use common sense" pva before lunch then ur ready to go after.
Work in a way that ur always getting maximium walls done even if it means u gotta go into another room to put a small wall on and run back and forth,always try to put as much on as you can once its second coated and flat u should be ok to wet trowel and polish up.
Once your capable at plastering just try to make the mixer a little runnier and go for more walls.