Knowing where to shop is a big part of living cheap.
For example, you don't buy groceries at Albertsons if you're on a budget. A concrete example: Today I got the grocery ads in the mail. Albertsons had, right on the front, that they were dropping their everyday prices, so hot dogs that used to cost $2.19 now cost $1.39. Thing is, I get that SAME BRAND, SAME SIZE package of hot dogs at an everyday price of $.88 at WalMart, and on sale everywhere once a month or so for $.79.
Likewise, we've done tours of all the local Thrift Stores and Rosses. They aren't all created equal, and knowing which thrift stores have good prices, and which have good products, is a big deal. One thing we've learned is that Savers and Ross stores that are on the edge of wealthy neighborhoods have good stuff (two reasons, I figure: good donations and fewer shoppers, since people living in those wealthy neighborhoods don't shop at the thrift stores). The Ross on the Strip here in Vegas is the best one in the state--huge and kept well-stocked with the latest of the fashions they carry.
I've also found that it's a good idea to know which stores mark things down. For example, Saturday night at Smiths on Flamingo and Jones in Las Vegas, I can almost always find dairy products that are 2 days inside their "sell by" dates marked down to less than half price. Since most dairy products freeze well, it's a way to buy and stock up on things I use a lot for cheaper than sale prices. Just last week I got 20 lbs of cheese for $1.75/lb. Since I follow the ads faithfully, I knew that was a good deal--cheese goes on sale here for $2.50/lb usually. So I bought it and froze it. I've bought and frozen dozens of eggs dirt cheap, too, from that Smiths. The Food4Less on Decatur and Flamingo is the place to go for marked-down candy and dishes (go figure!).
Knowing where to get things is second only in importance to the key to living cheap:
Know what a good deal IS.
You get that by studying the ads and paying attention to what you paid last time. But if you can't figure that bit of information out, you'll never live cheap.