So, why did I call marketing terms “useless”? Really, a marketing term “urban fantasy” or “cozy mystery” pretty much says it all, narrows the audience enough for it to be manageable and, most of all, sounds very smart. God knows I’ve been wanting to write steampunk just because I adore the sound of that word. (And I haven’t given up this idea, just as I haven’t given up an idea to write a heavy doorstopper book.)
These marketing terms are necessary for publishers and bookstores. They give next to nothing for you as somebody who’s trying to build a personal brand (and convince people to buy your books) from scratch, using a blog and perhaps a Twitter account as your tools.
Why?
Well, because people pretty much know what they like to read, in these terms, already. Sure, at some point you’ll mention your genre, but it cannot be the basis of your personal brand. You’ll have to be more specific. And no, I don’t mean that you should say you’re writing “steampunk mystery with a dash of coming-to-age romance” instead of “steampunk”. I mean that you need to be more specific about things people will really get from your books.
So you’ll need to figure out what are the recurring qualities of your work. For example, “fast-paced”, or “dreamy”, or “cinematic”, or “funny”, or “crazy”, or “sophisticated”. That’s not easy since you almost never write what you intended to write. Having written a teenage outburst instead of philosophical treatise… Well, it hurts, and it takes time and courage to recognize. If you have a trusted reader, this is where you ask for help, too, especially since your trusted reader can point to things that you thought were too obvious to mention.

The funny thing is that you don’t need to mention this in your blog at all. This is your hidden knowledge, your secret recipe. And you keep it secret because people who’ll read and like your books won’t always read and like them for their strengths. All you do is act like a person who wrote your stories, and truthfully so.
That’s harder, and also way easier, than it sounds.

Now, the brain-arrival-time has come for the whole personal branding thing.

I’m thinking that, if we’re looking at literary marketing, it’s pretty similar to that of any other product. A book appeals to certain audience, and that audience is who the author wants to talk to. It’s really that simple.
If I’m producing and selling pink fluffy purses, I’m going to have a website that says “Hi Sweetheart!”. If I’m producing and selling steel-toed army boots, I’m banishing the idea of “Sweetheart” from that website. If I’m trying to be smart and design pink fluffy steel-toed army boots, I’d probably say “Sweetheart, go kick their sorry asses!”. I am not doing a research on 15-year-old girls and conclude that most of them respond well to “Hello there”, because I’m not talking ot most of them, I’m talking to a select few, the ones who’d be willing to buy my product.

So, well, for personal branding a writer has to figure out what sort of product does she write (not “would like to write” or “should write”… there’s no market for whipcream that wanted to be butter), what sort of person is the reader of these stories, and what sort of language does this reader appreciate.
The good news is that if you’re writing what you really want to write, chances are your normal speaking voice is very much like the voice you should be using when talking to your readers. Eg if you’re a cynical person writing cynical stories, your reader wouldn’t mind if you were cynical in your blog. Or, if you are a cute person writing sweet stories, the reader who is nauseated by your cutiepie blog would not enjoy your books, so you don’t need to appeal to that reader at all.
The bad news is that there’s nothing harder than defining yourself and the stories you’re writing outside the useless marketing terms. But that’s, I guess, a subject of another post.