Go to the bathroom and eat before you go. There's nothing worse than having to pee while you're trying to thrift.
Shop mid-week if you can. Or find out when your favorite stores put out new merchandise. If you've got to shop on Saturday, do it early. Everything's picked over by midday. Same goes with garage sales.
Wear a dress or skirt (if you go in for that sort of thing), so you can try on bottoms under your skirt. Ignore the "don't try on" sign--we do and we have yet to be reprimanded. Of course, we haven't tried this in those fancy consignment shops or in other countries. We hear you can't even touch merchandise you want to buy in Paris.
Shop with a friend who wears a totally different size, or has a really different style, and spread out. No use competing with your buds over duds.
WHERE TO GO:
Trawl the fancy neighborhoods for garage sales. Look for signs, or check the paper for advertisements. And show up as soon as they start. Die-hard thrifters get there an hour beforehand (not that we recommend that). Try second hand or consignment shops in fancy neighborhoods too.
Find places that sell stuff "by the pound." You get more bang for your buck.
Travel to different towns, states, countries. It's a little sick, but try small towns that were once wealthy--like when people still took trains everywhere. Their stores are full of well-made, old-time clothes.