Guide to Civic Leadership Blogging (2005 U.K. edition)
How to use weblogs as an effective local leadership tool

How to blog effectively: Post short and frequent vs. long and infrequent

Long (more than a screenful), text-heavy posts to your blog where you need the space to explain are perfectly appropriate. Use the blog software's "extended entry" feature, if it has it, to only display the first paragraph or two. This gives people the option to read on if they're interested and makes skipping to the next post in chronological order easier.

But beware of falling into the trap of thinking that you always have to have long, substantive posts. It'll likely discourage you from posting frequently. Short, frequent posts help you maintain your audience. And they develop your blogging discipline.