Jason Cohen wrote a nice article about starting with blogging. One of the ideas he has about this is that you start with an article written by someone else that you like. Then you quote it and elaborate or reply to it.
This is a nice way to start blogging. The thing that often happens to me is the following. I follow this idea, but when I start writing I move so far from the original point of the article that it doesn't even matter anymore to the new blog post. Then I remove the quote from the top and have a whole new article. I still like to link to the article, but it just doesn't make any sense anymore.