Don't agonise over things that can easily be bought again if you decide you made a mistake.
Chuck out your oldest towels, bedlinen, pillows, cushions, clothes etc and start using any that you keep "for best", for special occasions or for guests. Again, if you feel later you don't have enough, this is not a big deal.
Look especially critically at old technology that can be replaced with digital equivalents, books, CDs, DVDs, radios, small TVs.
Get rid of all mass-produced vases, ornaments, pictures, Xmas decorations, candles, and the like.
For sentimental items, prioritise keeping ones which are not likely to get broken in the move or wear out over the next few years. Keep them all if in any doubt and just spend time packing everything carefully.
Don't forget anything in the garden or garage. Those boxes of used screws that might come in handy, rusty, blunt, worn out tools, the lawnmower that doesn't actually cut grass.