How to write a blog post

Do it like this: Joel on Software.

An appropriate illustration,
A useful topic, easily broadened to be useful to a large number of readers,
Simple language with no useless jargon,
Not too long,
Focusing on something that people have previously taken for granted,
That initially creates emotional resistance,
Then causes a light bulb go go off
and finally,
Causes the reader to look at the world differently all day long.