Some wise words from Mr Uku, he of Will Write for Cake fame:
The one thing a writer’s blog should never be is a marketing campaign. Because that, more than anything else will suck all the fun out of blogging. So stop worrying and have fun. Remember, blog because you want to, not because you think you have to.
Writers are frequently told that they must have a blog, so that they can build an audience and establish their brand. That's all fine. I've got no bones with any writer doing either of those things. In fact, I pretty much encourage it. But if that's all you're blogging for - to sell your wares - I think you'll run into problems.
Blogging is all about sharing. Sharing an opinion. Sharing experience. If you can share well - with context, thought and humility - you'll gather readers naturally.
On the other hand, if you mention your exciting new e-book in every other paragraph, you'll appear entirely disingenuous.
And that's no fun for anyone.