Agreed about "the parent is the parent."
I usually try to give warnings before "laying the smack down" (read: putting the child in time out/"naughty corner") the first time. I believe the kids need to know what the rules are before they are punished, rather than after; otherwise punishment seems arbitrary. The very first time my son hit my daughter, he received a warning (and vice versa). Now, they don't get warnings - you hit your sibling, you're off to time out.
I've also tried to be big on showing love while punishing. That may sound weird, but here's an example - my son hits his sister. I come to take him to time out and he starts crying "I don't want to go to the corner! I love you daddy!" Of course, he's just trying to weasel out of his punishment, so I tell him, "I love you, too - which is why I wish you hadn't chosen to hit your sister and receive the punishment that goes with it. I don't like putting you in the corner, but you know the rules, and I can't break the rules for you." I left him in the corner for a couple of minutes, then came and gave him a hug and said, "I love you, but I don't love hitting. Please go give your sister a hug and say you're sorry."
I try very hard to dissociate my dislike of the behavior from my love for the child. I always say the behavior is bad, not the child. ("Hitting is bad" instead of "you're a bad boy for hitting.") I always tell my children I love them, both when they're acting well and when they're acting badly. I praise the good behavior, too ("Sharing is good, thank you for doing it.") but again never make love contingent on behavior.
My kids aren't perfect, but they use "please" and "thank you" and "you're welcome" a lot. When one of them gets a cookie, drink of juice, or whatever, they always want two. You give my daughter a cookie and she'll say, "one for Nathaniel" - give my son a cookie and he'll say, "I need one for Leilani, too, please." And they actually DO share and watch out for each other that way!
Of course, my daughter, being two, is prone to fits when the world doesn't work the way she wants (when PBS has a show on that she likes and the show ends - say, "Bob the Builder" - she freaks out). She's also a very messy girl... we joke that she doesn't just eat her food, she wants it to be a five-senses experience... she loves to play and dig in the dirt... she loves playdough, and especially loves squishing it in her fingers and then pulling it into a million little bits (our son, by contrast, is a neat freak who could eat with a fork with not a crumb spilled by the time he was 18 months and who hates getting dirty). So she's a handful - not because she's ill-behaved, but because if you turn your back on her for even a minute, she'll have dissected something. She exhibits the "I have to tear it down to its constituent parts to understand how it works" curiosity (and I don't want to discourage that; she's not destryoing just to destroy but she does check out how things work and occasionally tries to put them back together - besides, I'm somewhat the same myself). She also has a very short attention span/patience, while my son can lock into a task for hours (literally; while his interests are a little more diverse now, from the time he was about 10 months until he was almost 3 years, he spent at least four hours a day shooting baskets on a little hoop set we got him when he started grabbing my basketballs and trying to dribble them - he's already able to dribble a full-size basketball up and down a regulation court with no double-dribbling, and can pass and shoot the full-size ball from about 10 feet away on a 6-foot hoop; I should note we aren't requiring him to play - I had little athletic aspiration myself and am making very sure not to project any I do have onto my kids and becoming a "bad sports parent" - he just loves the game, as he grabs his ball from his toybox amid scores of other toys with no prompting and entertains himself for hours on end).
So my daughter has to be watched like a hawk, not because she's malicious, but because of her personality... she'll zoom from place to place dissecting everything (though she knows not to touch my RPG bookshelf)... we call her our little tasmanian devil, because she's just a little tornado of energy. My older son... well, give him a computer or a basketball and hoop or paper and pencils, and he's okay to be left alone for an hour or so. My youngest son is still in the "eats, poops, and spits up" phase, so even if he wanted to get into trouble when we leave him alone, he's as yet physically incapable of doing so.
One important thing to keep in mind, though... no two children are alike. What works for Child A may not necessarily work for Child B. And don't associate unruly children with bad parenting - there are some occasions where the parents have tried six ways to Sunday and nothing works. In other words, I believe bad parenting leads to unruly children, but the converse is not true. I'm discovering that with my own kids - what worked for my oldest son doesn't always work with my daughter (and vice versa). So take as many suggestions as you can that fit with your parenting philosophy, try them out, and don't be afraid to discard the ones that don't work with your child just because "so-and-so said this worked great with THEIR kid."