In my capacity as proprietor of what may be the oldest continuously operating personal web site in Miami, please allow me to share my experience in how to achieve success in this increasingly crowded field. As will become obvious, this is a case of "do as I say, not as I do."
First, define success. If you equate success with making big money, step away from the computer and go back on your meds. You will never be a successful blogger. If your success is measured in the satisfaction of seeing your words appear magically on the computer screen of at least one complete stranger, then just publish a page and congratulations: you are a success. But if you measure success through accumulating an increasing stream of readers and building a strong community, read on.
Content is next. What can you offer for people to read? The simplest thing to do is to pick a topic about which you are passionate, and write exclusively about that. It doesn't really matter what that topic might be, although porn and politics seem to gather readers the fastest. Just don't screw around with writing about whatever strikes your fancy. Like it or not, blogs are TV shows, and your audience wants to know what to expect every time they tune in. If you write about nuclear physics, no-one wants to see a picture of your baby. If you write about babies, nobody cares what you think about global warming. That's not what they paid for with their time.
There are four exceptions to this rule. If you are a pioneer of the form (i.e., your blog started prior to 2000), then in all probability you already have an audience which will read you out of habit, even if you suck. Should you be blessed with a unique and compelling authorial voice, then you might be able to build up a blog about nothing in particular, but it'll be difficult. If you are a teenager writing about teenage life, other teenagers will form your audience, so nothing more specific is required; teenage life is effectively your topic. And if you are sexy, have a webcam, and lack inhibitions, people will flock to your site to pretend to read your godawful poetry. These are the only exceptions I have found.
So assuming you are operating under a reasonable definition of success, and you have worked out a topic, what else do you need? Content, particularly high quantity and frequency of posts. Audiences do not care that you've had a shitty week at work, when they load your site they want to see something new. If you post short links to items of interest you should post several a day, while daily essays can get by if they are sufficiently long. Since most of your audience reads while they are supposed to be working, you can sometimes get away with skipping weekends, but if possible post at least once a day. Otherwise people will find someone new to entertain them, and good luck getting them back.
Getting the audience to your site in the first place is tricky, particularly in these days when everyone and their budgie has a blog. If your subject is obscure enough then the miracle of Google will eventually bring people to your digital door. Trust me on this: nothing is too outre to fail to find a couple of hundred like-minded souls on the internet. Nothing. God help us all, nothing is too twisted, perverse, or obscure to have a fanbase on-line.
But if you are writing about something a little more common, such as politics, technology, or media reviews, you'll have to work hard for your piece of that pie. First, visit your competition and leave good comments. The most significant difference from traditional publishing (other than cost of entry) is the immediacy of feedback, and the communities of like-minded people who form around popular sites; those communities spread. If your comments are clever and smart and include your web address, you will get visitors. With luck you'll get links from the popular blogs to your own site, and then you are off and running.
Lastly, be very, very lucky. We're talking about Lotto-winning kind of luck here, folks. Technorati is tracking 24.7 million blogs, and those are only the sites they know about. With all that competition, you're going to need more luck than anything else to succeed.
And that's it! Oh, what's that you say, why didn't I address writing skill and style? Well, I could be generous and say that I assume you have that covered if you are interested in publishing. Or I could be flip and say it doesn't matter because blogs are the new TV and quality never succeeds. The simple truth, though, is that while writers and sites displaying creativity and skill are beautiful and deserve wider recognition, quality is rarely enough to qualify you for success. In a perfect world it would, sure, but why should weblogs be any different from any other creative endeavor?
Still want to publish a successful blog? Then go forth with my blessings, children! Be funny and insightful and creative and successful, and try to have fun doing it. None of us are getting rich, so we might as well have a good time.
And if you do become successful, give me a link back, damn it!