When you buy a cast-iron pan, clean it with steel wool if necessary to remove any light rust, particularly if it's second-hand. Rinse the pan and dry it, then brush a film of vegetable oil inside and out with a paper towel. Finish the process on the barbecue if you have one; crank the heat, put the pan on the grate, upside down, and leave it for an hour or so. (You can also use a 250-degree oven, leaving the pan in for at least a couple hours; be prepared for a bit of smoke.)
To maintain the pan, don't use soap unless absolutely necessary; scrub it with hot water and a stiff brush or copper scrubbing pad. Dry once it's clean, and then rub with a thin film of vegetable oil. High-acid foods such as lemon juice and tomatoes are best left to stainless; the acid will pull out some of cast iron's seasoning.
For delicate foods such as pancakes, use a lower setting than you're used to (cast iron retains a lot of heat) and give the pan time to heat evenly. But for meat, burgers and greens such as sautéed rapini, let 'er rip.
After you put your meat in the hot pan, go pour a drink or something: It needs a little alone time to sear. Then it will "release" from the pan's surface, and you'll be able to turn it without sticking.