There are many Blogging platforms available and many are free. Here are the most popular:

Blogger by Google (free, hosted)
TypePad by SixApart ($49.50/year, hosted)
WordPress.com (free, hosted w/fee)
WordPress.org (free, unhosted)
MovableType by SixApart (free for personal use, unhosted | $150 for business use, one time fee, unhosted)
blogging systems Specifically for real estate. See web site for programs.

I use MovableType (as a business user) and host it on my own URL web servers.

Blogs are a reflection of their authors. What you do, what you say, your opinions, sharing of experiences, providing content that consumers want and need and how you present it are the most important factors in a successful Blog. Here are the do's and don'ts from some of the best:

The Do's...

• Write from the heart.
• Be open to criticism (you'll probaly get some).
• Express your honest opinions.
• Find a niche.
• Use keywords in your article titles.
• Read other Blogs and comment on them (provides links).
• Get listed in Blog aggregators (Technorati, del.icio.us, etc.)
• Be patient, it takes time.
• Frequent short articles are better than an occasional long one.
• Have a long article? Break it into shorter tidbits.
• Make your topic categories keywords.
• Write a series...keep readers coming back for more.
• Read...then comment on what you read...in your own words.
• Link to other Blog articles you read and publish an article on it with your opinions.
• Start a Blogroll of your favorites.
• There's s lot more...research the web for blogging tips

Then the DONT'S...

• Don't self promote! This isn't the place for it. Consumers want to get to know the real you through what you provide in your Blog articles.
• Don't use canned content...it's not unique and not you.
• Don't copy others content...bad...bad...bad. Respect © notices.
• Don't do property advertisements...this is debatable (I do).
• Don't censure...people won't comment
• Don't publish multiple Blogs...do one outstanding Blog (I violate this one)
• Don't wait too long between publishing articles...Blogs get stale fast
• Do not name names in negative context...use: "a recent client" or "an agent I recently dealt with."
• Don't have others write for you.
• Don't give up.

A final note: Blogging is not for everyone. It takes a tremendous amount of effort, stamina and creativity. Blogging is hard work. I have seen many blogs started and then abandoned after just a couple of articles. It was either too hard or the return was not immediate.

Here are a couple of good links to read from ParticleWave:
Why Start a Real Estate Blog? and
Promoting a Blog on the Search Engines.