I do this a couple of times a year and love it!
I often get a friend round to help and we drink wine and she takes anything I don't want but she does - then I return the favour another time.
If you are prepared for chaos then follow my method
Take out clothes by 'type' .I find it's easier to put up a 'temporary' clothes rail, but you can use your curtain rail if not.
So say, start with dresses. Have a good look / try them on, and sort into keep in wardrobe, keep in storage and give away.
Once it's pared down a little have another think then bag up /hang up/ store away as appropriate.
Then do the same with everything else.
Pay attention to if there are things you love but don't wear because they need altering/ mending, i.e loose buttons, too long trousers and put in a separate pile to be fixed.
Then once you've got a streamlined wardrobe you can look at what will look good together (always the fun part)
And don't forget to sort out your bags / shoes/ scarves etc as sometimes just adding a belt can make you love a dress you havent worn for ages again.