Are you on pinterest or instagram? There are lots of pins and many instagram accounts that would help you.
First piece of advice is to break it down; don't think about ALL the things you have to do at once or you'll become overwhelmed and it will paralyse you.
So you start with one area, say coats for example and separate into don't want/have holes/too small etc, want but not weather appropriate/special occasions, want and suitable for current season. Go through this with all your different areas that need decluttering.
Then you should have a pile of things to get rid of either by taking to tip, selling or donating, a pile of things you need or want to keep but don't use all the time and therefore need storing somewhere, and a pile of things you want to keep where they are.
From there you can organise collections, donations, giving to family and friends, selling or giving away through FB marketplace/ebay/vinted etc.
You can also now look at what you have and purchase any boxes/caddies/vacuum bags etc and think of where you are going to store them. Attic? Basement? Cupboard under the stairs? Garage?
Hope this is helpful, signed a decluttering and organisation enthusiast. 