1. Find a niche and stick to it. Most successful blogs focus on a single topic. Some rely on the blogger’s unique voice and charismatic personality to unify otherwise unrelated posts, but this is hard to do. Whether you’re blogging about copywriting or self-development, it’s much easier to find an audience once you tap into that community.
2. Put your personal spin on the topic. I’ve found that what works well for me is to cover an aspect of writing (maybe it’s dealing with editors or brainstorming for ideas) and work in personal anecdotes. I try not to dwell too much on the specifics of my situation and include takeaway points that readers can apply to their own writing careers. People usually read blogs because of the blogger’s personality, so let yours shine through.
3. Commit to posting regularly. Like training for a marathon or practising a musical intrument, blogging gets easier the more you do it. You’ll develop a writing style, get into a schedule, and pretty soon the ideas will be flowing out of you at 1 o’clock in the morning (or maybe that’s just me). Bonus: readers will keep coming back for more if they see that you update regularly.
4. Link to other like-minded (or unlike-minded) bloggers. This is a good way to get the conversation going and show that you’re a good citizen of the blogosphere. When you’re stumped for a post idea, you can find an interesting post written by someone else in your niche, link to them, and write about why you agree or disagree with their opinion. Voila!
5. Get your own domain name. As previously discussed, it looks more professional to have your own URL without wordpress.org or blogspot.com attached to the end. When I bought my own Blogger domain, the transition was pretty seamless, but it isn’t always that way. Save yourself a giant headache and buy a domain now. That way you won’t lose traffic or incoming links later.

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Source: http://www.urbanmusewriter.com/2008/09/10-tips-for-new-bloggers.html

“To help make sure you have enough to write about, set up a Google news alert to receive e-mails about stories with keywords from your industry. That way, you’ll get news about your field in your inbox automatically. Link to those articles on your blog, and write about whether you agree with them and why. Describe relevant professional experiences of your own. Predict how the matter at hand will affect your industry in the future”.

Source: http://hotjobs.yahoo.com/career-articles-blogging_your_way_into_a_job-807