I just did this due to moving cross country, and reeeeally needing to downsize to save moving costs, so it was ruthless.
I did the first round about a month before moving, one garbage bag for the bin, one for the op shop and one for the buy/sell page. Went nuts for the week and then left it for 2 weeks, and went back and did it all over again. I found that stuff I was doubtful about or could find a sentimental reason to keep, went in round 2. It was much easier the second round to get rid of things knowing I had not used them during that period.
If they can easily be borrowed/replaced/sourced second hand later IF I need them, they went. And straight to the op shop the next day. No mess, no fuss, and whilst I got rid a MASS of things I *could* have sold on ebay or gumtree and made some money, it was soooo much better for my head space to have them gone straight away and out of the house.

I am having the removalists come in the morning with all our stuff, and will be culling again, round 3, while unpacking and I am sure I can get rid of a third of it.

I am a bit of a hoarder, so I need to do this every year or so to get rid of it all.