Empty it completely first
Pull everything onto the drive and sort into keep sell donate and dispose. Working around what is already there never produces a real result because you never see the whole picture.
Zone the space
Give every category a fixed home. Tools on one wall garden equipment near the door sports and bikes together seasonal storage high up. Things return to a zone far more reliably than they return to a vague area.
Get everything off the floor
Wall mounted racks pegboards ceiling hoists and heavy duty shelving multiply usable space. Clear stackable boxes beat cardboard because you can see contents and they survive damp.
Store chemicals and fuel safely
Paint solvents fuel and garden chemicals belong in a locked ventilated cabinet away from the boiler and out of reach of children. Never move fuel or gas cylinders in a removal van because they are excluded from every transit policy.
In short
Empty it fully zone it clearly lift everything off the floor and lock the chemicals away.