i recommend a week or two course just to learn basics, using hawk and trowel, how to apply, how to mix, different types of plaster etc etc, just so u can start and not look a total mug who dont know jack.
but dont buy into the crap about become a plasterer in a month.
your dreaming if you think you can go on ya own or do site work so quick.
i done a two week course then got taken on as a plasteres mate/labourer where i get to do a bit and assist a experienced plaster in all types of differnt of situations and all types of repairs and all the tricks of the trade, and just the whole way they work, down to bucket systems

, i can ask all the questions i like and he always explains y he doing this and y this is this etc etc. i witnessing things on the job that u will never see on a course (on domestic work). plastering is not all about the glamour of skimming :-/
people on the course i done reckoned they were gonna go on site after 2/3 weeks which is so unrealistic, you have to do 50sq meter at least, where all we done was a wall about 4 sq m. :'(
i know i could plaster a room on my own and the final look would be good but i know i need to be 10 times faster where ya on ya own, it wont happen overnight.
my gaff said people do these courses and get a private job but the phone soon stops ringing when they get a bad rep, cause they dont know jack.
courses r good for learning basic, but nothing more ;D like any job on the job experience counts
start at the bottom and work up mate its the only way

cause unless u can wait for private jobs that will all be skimming a box room, u wont get anywhere :'(