For those of you who have done some research on publication and read blogs dealing with the subject, you've probably already heard the concept of building a platform. It's popular - I know of one book on the subject, and I'm sure there are plenty more - and can be made to sound quite frightening, but the basic idea is that of planting yourself deeply and squarely in your field. In writing, this means marketing to your audience: fiction or nonfiction; middle-grade, young adult, adult; men or women; fantasy, historical, dystopian, what-have-you. This is what makes "knowing your audience" so important, because marketing your young adult dystopian to middle-aged fans of World War II history is not only silly, it's also a waste of everyone's time.
Building a platform can take many different forms, but one of the most common nowadays is starting a blog. It has a number of advantages over sites like Facebook or Twitter; authors can write lengthier posts on weightier topics (it's hard to be weighty in 160 characters!), but still interact with readers. A blog also allows more of the author's voice and personality to come through and gives potential readers a better idea of what the author's book might read like.
But there are very rarely advantages without some disadvantages. While blogs are fun at the start, when ideas are simply brimming in our minds, they can lose their charm fast and leave us quite disillusioned. If you want to maintain a blog and use it as a platform, you have to be dedicated to it. You can't just quit when the ideas won't come; you have to go after inspiration with a club, as Jack London would say. ...Did say, even. Blogs are also quite a bit of work to maintain, unlike a Facebook or Twitter account (although I confess I fail in the latter respect). You can't just log in, type a one- or two-line comment, submit it and go your way. You've got to make time to sit down and think out, and type out, a post of at least a couple paragraphs and some worthwhile content.
Content, too, can be a difficulty. Glancing over the blogs I come across, I find an alarming number of ones where the writer seems to have started and then lost either interest or ideas or both. This may mean that the last post was put up in February 2009, or it may mean that the writer has struggled along with a post per month on random and unimportant aspects of their lives. Readers learn about the author's fifth cousin who has a deathly illness, or the author's new poodle-greyhound-Great Dane puppy, or sometimes hey! look! my new book released: whaddya know? This is obligatory blogging combined with purposelessness, and it results in boring reading and a jittery platform.
If we want to undertake a blog for anything more than a sort of public journal (which I confess I don't understand), we have to think about it beforehand and use some sort of plan and schedule in the process. It isn't necessary to post every day, or every other day, or even every other third day; in fact, posting too frequently, especially if the blog doesn't have more than one contributor, can get repetitive. But neglecting the blog for weeks on end has the same effect. It's good to have in mind a general idea of how frequently you want to post. You don't have to stick to it religiously - at least, I know I don't - but it can be helpful to know what goal you're working toward.
In the interest of building a platform, it's also important to know what topics you want to be posting on. Again, I don't recommend setting this in stone; some people like to set a schedule of posting on one thing on Mondays and another topic Fridays and pictures on Sundays, but that doesn't suit everyone. Just make sure you know what you're blogging for and what topics you are best suited to write on. If historical fiction is your genre, perhaps research (but I'd advise you to take this in small doses, because out of context it can be found dull), incorporation of historical characters, and general writing tips. Don't spend posts rambling about things that readers of the genre don't care about, like your poodle-greyhound-Great Dane. That's what spots like private Facebook accounts and Twitter are for.
Spontaneity is fine; it makes the blog more fun.
Randomness is not; it is the mark of an unfocused mind.