You'll need a neck brace for the stiff neck and line up a good massage for the aching shoulders. Eye wash to clear all the drippings that will inevitably land in your face just as you turn back towards the job. You could try wearing goggles, but they'll just steam up and you won't be able to see what you're doing. Mix up double what you need because at least half of it will end up on the floor, then when you step down off the ladder you'll tread in it without realising until you notice all the footprints in the hallway carpet. Sorry to be a little cynical, I've got a similar job to do myself soon only mine's in a room a little larger than yours (approx 2.6m x 1.8m).
To be honest I can't really offer any pearls of wisdom, plastering a ceiling isn't that much different from a wall except it's a little more awkward as you'll be working overhead. When working from a ladder, I find it easier to put the plaster on in a long sweeping arc, move the ladder then repeat until it's completely covered. Never mix up too much at once, as the chances are it'll start to turn before you've used it all up. It always seems to take longer when doing a ceiling. When polishing the plaster, I use a little flower spray bottle which puts a fine mist of water onto the plaster, I've tried flicking the water on with a large brush, but it doesn't work as well for me.