From Merlin Mann. Visit the link for an accompanying 70 minute video (It enlightened and entertained me, but I would only recommend it if you are or aspire to be a *serious* blogger, whatever that means). (Hat tip: Hugh Hollowell.)
You would be hard pressed to pack more substance into a smaller space, but I would add a few more recommendations. Of course it is going to be different for everyone and depends on what you are trying to accomplish, but I try to blog by the following principles:
Know why you are blogging.
Dare to be wrong, often.
Study at least two or three bloggers you admire and aspire to match them in quality.
Separate the writing and editing process.
Pledge not to check traffic stats more than once a day.
Inject personal narrative into the blog, but not a lot.
Read at least as much as you write.
Post things that interest you even if they might not interest your readers; your audience will find you.
Have a system; "I'll blog when I feel like it" does not work.
Above all, get to know your loyal readers because whether or not you started this way, they will become the reason why you blog.
