When you pack up at home put the table in last, so it is first out.
Work as a pair when unloading, one unpacks and one arranges and sells to the dealers/ chancers that will hover and pounce first thing. Don't end up with both of you head first in the boot while half you stuff takes a walk off the table.
Have some sheets of plastic, clear is ideal or at the very least binbags to hand to cover stuff if it is showery.
Pasting tables are OK but do tend to give way under piles of books and ornaments, plastic patio tables are a bit sturdier.
Have a float ready and keep cash in a bum bag or pocket not in an ice cream tub on the table. You won't need coppers unless you plan to sell stuff for 99p. Stick to piles of silver and a few pounds and fivers, people will arrive straight fromthe cash machine and be looking for change of £10 and £20.
Definatly discuss prices and make a list of important things if not pricing individuly, you don't want to come back from the loo to discover DH has sold your best vase for 10p to a kid.
I found a parasol was very handy, you have to have it higher than normal so it is above poking eye level, I filled the base and set it behind the table, so it kept me and the stuff in the middle of the table dry.
If you are going to be on grass or wet ground again binbags are handy to put boxes on top of full of cheap stuff like soft toys, boxes get soggy quickly and fall apart.
Chairs are better than perching on an open boot for hours, a higher stool is even better as you can see what is going on.