Oh I'm the queen of decluttering.
Get 3 boxes: Label them Keep, Throw, Charity. And then take one section at a time, even if that means one drawer or one cupboard. Don't try to do too much as it will be overwhelming. If you've not thought about or used something in 6 months then pass it on or whizz it. We keep and accumulate so much over the years and honestly, we don't need it. Also get rid of any repeated items....you're really don't need 7 tin openers

Get everyone involved because it feels so good afterwards.
If you've got a shredder make yourself a nice pile of unneeded paperwork and do it at night as you're sat comfortably watching TV or rip it up and put it into a bowl of warm water, let it soak and when it's maliable squeeze all the water out. It will eventually harden and whatever was typed/written on it will be gone.
I'm a big fan of containers, particularly in the shed. I decant any paint leftovers into a jar and label which room they're from. I have containers for garden items, paintbrushes, screws, nails etc all labelled and stacked neatly.