I am lifting our onions just now. After lifting they are laid out, ideally in the sun, to finish drying off - say a day or two. I then store them in a mesh bag in the shed, hanging in an airy spot. Keep an eye on them through the winter in case any start rotting.
Alternatively, look at this blog by Moongrower on how to plaite your onions:
http://www.growsonyou.com/moon_grower/blog/17159-how-to-store-your-onions-over-winter-and-other-tips

Thanks for the advice
Weebeth