The eejits next door to me did a much better job than I did, so here's their method :). First they got a strimmer, and strimmed down the long grass etc. (I would have begun to build a compost heap with this). Then they used the blades of spades to cut the weeds right down to the earth, so there was barely any green to be seen (too much rhyming in this sentence, sorry). Only after that did they mark out basic beds, and paths, and dug the borders of the beds so it was really clear what had to be done next. Then they got a digging party going and each took a bed and took their own time digging it over and removing perennial roots. If you've got the labour, it's a good way to do it. Remember rotavating doesn't remove roots so you're going to have to do the back-breaking work anyway.
As for weedkiller there's different types and different choices. If you want to be organic it's a no-no from the get go (Sorry! I seem to be possessed by the spirit of Dr Seuss today). If you're not bothered and you've got enough labour you may as well do it the hard way and you can make the organic/not organic decision later.
