Since most of the new people are on here live in cities, the advice I give out most frequently ends up being specific to those backgrounds and environments.
Don't get chickens if you're not prepared for the reality behind the cuteness. Chickens get sick, injured, or die, and eventually you're going to have choices to make that you don't want to. They're classed as livestock for a reason—they aren't like, say, dogs, where a few vaccines will keep you almost entirely out of trouble. I'm not saying they shouldn't be kept as pets, but rather that it's not in their nature and so they still behave like barnyard animals, even when humans try to prevent it.
Start with good birds. Feed them right. Have a plan for when one inevitably needs to be put down. Last, but not least, GIVE THEM SPACE. I can't tell you how many postage stamp coops I've seen. 4 square feet of space in the coop and 10 in the run is still a minimum, IMO, and your birds will be far happier if they have more. They're ranging creatures by nature. Ever seen a chicken take off as fast as it can and just run and flap for the sheer joy of it until it becomes airborne? Doesn't make me much inclined to pen them.
If you want a good, productive flock from which you hatch your own replacements, there are a few more things. Ideally, you should keep only the top 10 or 20 percent of your birds. That means you buy a hundred chicks and butcher all but a dozen or so. I think most people would benefit simply by culling 20 percent. Don't keep sick birds, don't breed sick birds, and don't sell sick birds. Worm resistance, louse resistance, and feather quality vary bird-to-bird, so if you select for these things, or for anything else you prioritize, you'll get it. In the long run, you'll end up with a flock that takes much less maintenance if you don't waver in breeder selection.
Most hatchery stock isn't bad in the aforementioned departments. But you'll still end up with a few that outshine the rest. Keep them. Breed them.
