From the ABC's of Beginning Your Blog by Karen Klein at  Business Week with a hat tip to Kevin O'Keefe at LexBlog.

1. position yourself as an expert and demonstrate your experience.
2. the information in your blog should directly help your market solve a problem or address their wants and needs
3. read other peoples' blogs and get a handle on what they're doing
4. reading blogs within your industry will give you a sense of what niches are underserved and will help get your own creative juices flowing so you can write authoritatively when it's your turn.
5. initiate conversations with other bloggers by commenting on their blog entries
6. when you set up your own blog, [they will be] more likely to link to you, and send their readers
7. you need to blog regularly, under your real identity with an authentic voice
8. be sure that you have something personal and interesting to write about.
9. cross-promote 
10. consider adding a blog to your existing Web site
11. for experimenting with a blog, there's nothing more simple than setting up one on Blogger.com, operated by Google 
12. use a "tagging" service, such as that provided by Technorati.com, to help advertise your blog
13. a tag is basically a label you give your blog -- say 'professional services.'
14. anyone who uses Technorati and has subscribed to that tag will receive a notification of your new blog entry on that subject
15. encourage your customers to subscribe to your blog's RSS feed.