Plan your route based on the sites you want to see and the vide greniers that are going on while there. Be aware that vide greniers are canceled if it is raining too hard but brocantes are always open...well, almost...most shops (not just antiques) are closed Sundays through Monday late afternoon and during the lunch time from about noon to four. Flea markets are usually on Saturdays and Sundays. Watch out for holidays! Who knew that the Feast of the Assumption would entail almost a whole week of shops being closed!! The French (as most Europeans) take any religious or civic holiday very seriously and combine days to make a very long weekend.
Pack your bags...I packed an expandable medium sized rolling bag containing nothing but bubble wrap inside a large rolling bag that I paid $3 for at the Goodwill. Then I packed 2 sets of clothes, underwear, nightie, extra pair of shoes and toiletries in another bag inside another big Goodwill bag. Don't waste room on lots of clothes..take my word (and Rick Steves'), you won't wear them and you'll kick yourself for lugging them all over. I used the second smaller bag for a carry on on the return trip so I had something to put breakables in.
Bring extra friends (preferably relatives so I could boss them around!)...the kind who are only there for sightseeing and not buying!! They were my mules at the end of the trip.
Fly to France, see Paris on a double decker bus for one day, and then start shopping! I flew Iceland Air and got an amazing airfare. My advice would be to arrive on a Friday, see Paris and head to the Paris flea markets on Saturday and Sunday.
Take the TGV train to a large city outside of Paris (Lyon is big enough, one of the largest markets in France and lots of shopping there too!). Why take the train out of Paris you ask? Save hours of being lost, being caught in horrendous traffic, and wasting precious travel time. The TGV is 2 hrs to Lyon where driving could easily take you 6 frustrating hours!
Rent a car and start shopping. Plan on being lost for hours on end but I used that time to scout out antique stores. I found the junky ones in the middle of nowhere with stuff piled in the yard and the barn door wide open to be the best ones. Just like here at home, if I made a pile, I got a better price on the whole kit and kaboodle.