Blogs allow your readers to comment and interact with you. It's let formal than a website and your readers can stay informed of the updates via RSS feed (http://www.whatisrss.com).
Update often; let your followers hear personal stories about what is going in your ministry. Keep the postings shorter and add pictures to create a deeper level of connection with your readers.
Keep your blog simple, clean, and easy to read. Don't overpower your readers with too many graphics and a distracting background.