What everybody said.
I have a blog that's now three months old! I'm so proud, but I keep working it hard. Here's the
Retrospective post. And yet the work has just begun.
My advice:
Work hard, work very hard. This means you have to passionately care about the subject.
Three months is the deciding point. Many blogs die before they reach this age. Work past it.
A new blog from someone unknown needs lots of good content fed to it; that way you develop voice, audience, and search hits. Since I post roughly twice a day, and of late have been posting at least one semi-contentful to mostly contentful post per day, I had enough material at the 3-month mark to do a retrospective. (Which has been helpful in letting people dig into older material when my blog was a lot less visible.) Content is key, lock, barrel.
Offer subscription options through a feed. And do full feeds. Yes, full feeds mean that your subscribers won't hit your site directly all the time, but on the other hand, they have developed a more intimate relationship with your site through the feed. All good.
Get out there and get your blog noticed without being spammy. Post to the "Did you update your blog?" thread with enticing article titles. Even more importantly, participate on forums and blogs that fit within your audience niche and have a signature that links back to your site. That has gotten me more traffic than anything else. If you have plenty of content, on posts you can start to offer that content when it's useful to other people. (Like this one.) "Build it and they will come" only works on Twitter.
Get your best content up and visible. Clean up your sidebar. Indicate clearly what your site is about in the top header so that people visiting from StumbleUpon can soon see if they want to stick around or not. Organize; people don't have time to wade through.
Learn how to use statistics gathering packages: Google Analytics, Feedburner, and I strongly suggest if you don't mind spending $20 a year or so, Performancing Metrics. Especially the latter will tell you in real time how your site is being used so you can locate content bottlenecks. Google Analytics is great for long-term analysis of what content works and what doesn't.
Read at least Problogger.com. I also suggest Skelliewag's blog and her new blog Anywired.
Work SEO (Search Engine Optimization). Almost no one outside the professional blogs does. This results in 25% to 50% of my traffic through search each day. This means specific titles and all that. I don't even try all that hard
(And you shouldn't drop so many key words as to be annoying.)
Don't do ads. Crazy, but true; new blogs aren't going to make enough money. Find other ways to make money with a blog--indirect works best. Me, I'm using my blog as a learning experience and as a way to get examples of my work up somewhere. (I'm planning on plenty of review work.)
Consider a blog an investment. Don't be afraid to drop change on it.
Be nice to others. Network, network, network. And then network some more.
My audience numbers are not very impressive right now, because it takes a long time to build it; maybe a couple hits per day if I was lucky in October, to 10 hits per day in November, to roughly 20 hits per day (averaged out) in December to now. Counting my feed audience, it's more like 30+ unique readers per day. I want to hit 100+ by November.
But in the end, I want to be useful to people. That means good content, unique voice and view, and letting people know about it all. That's the only real motive that has mattered for me.
Blogging is hard work. Don't let anyone tell you that it's not. If they snigger at you (yeah, it's like people who think writing is easy) then SHOW THEM ALL.
One last piece of advice--it's not just content. It's also passion. Because passion will drive you to make good content and get the word out. Don't estimate it.
PASSION!
ahem. but that's just me. heh.