Get hold of a strong large box, plus two large bin-liners. Mark one bin-liner 'rubbish', the other with the day's date.
Starting at one corner of a room, check every item (including cupboard contents), putting rubbish in the appropriate bag, and all items you know you won't be using in the next three months (including clothes) in the dated bin-liner (you may need more than one dated bin-liner!).
Put any items you're not sure about in the box.
Then seal up the dated bag(s) and put away in a safe, dry place.
Dispose of/recycle the items in the rubbish bag/s.
Go through the box of odd items and find places to put the ones you really want to keep. Keep this box as a ‘limbo’ to put all subsequent items that have no immediate purpose or place, but which you cannot bring yourself to throw away. If/when it gets too full, savagely sift it and dispose of some of the items (or put them in a 'dated' bin-liner!).
If a year passes without you missing the stuff in the dated bin-liners, you almost certainly don't need the stuff. Find someone who does, or recycle/dump it.
Repeat as necessary.
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