Underestimating how much you own
Almost everyone does this. The loft the garage the shed and the cupboard under the stairs are routinely forgotten and they are often a third of the load. An accurate volume means the right vehicle and a price that does not move.
Booking too late
Fridays and the last working day of the month sell out first. Booking four to six weeks ahead costs no more and gets you the date you actually want.
Packing boxes too heavy
Books go in small boxes bedding goes in large ones. A box nobody can lift safely is a box that gets dropped and the contents pay for it.
Assuming everything is insured
Check the level of Goods in Transit cover and whether any single item exceeds the per item limit. Declare high value pieces before the day rather than discovering the limit afterwards.
No essentials box
Kettle mugs tea toilet roll phone chargers a torch basic tools and medication. Pack it last load it last and you will thank yourself at nine in the evening.
Forgetting to redirect post and update addresses
Set up a Royal Mail redirection and work through the list of banks insurers DVLA GP dentist and employer in the fortnight before you go rather than the month after.
In short
Measure the real volume book early pack sensibly check the insurance and keep an essentials box with you.