From the blog: http://teachingcollegemath.com/?p=1898

Set up a blog using Blogger or Wordpress.  You should make at least six blog posts of at least two paragraphs each, using appropriate spelling and grammar.  The mathematics in your posts should be correct.  Blog posts should focus on what you have learned, what you’ve struggled with, or what you’ve found to help you learn.  Posts can discuss learning in class or out of class, but must relate to the current topics we are covering in the unit.  You should not refer to specific chapter or section numbers in your blog posts, and if you mention an activity from class, please use enough detail that a 3rd party reader would understand it.  Here are some specific details:

• Blog posts should be spaced apart (not all at the last minute).
• Your blog should include an appropriate  title (not just Maria’s Blog)
• Your blog should include a profile (picture and brief bio). This can be fictional if need be.
• Your blog should contain a “blogroll” with five of your favorite educational blogs.
• Your blog should contain a list of tagged topics or categories.
• Your blog should contain four images (or embedded videos) and should contain at least six links to web resources that you’ve found yourself.
• Links to web resources should be properly “clickable” within the text of the post (not just a pasted URL).
• Each post should be tagged with appropriate keywords.
• You should make at least six comments on the blog posts of other students.

I think that the nature of the blog (what to write about) needs to stay as open as possible, but the fine detail of the assignments is difficult to assess if the quality of blogs varies wildly.   If you choose to try an assignment like this, I highly recommend a table-style rubric (like the one below) to keep track of where you are assigning points.

I also found it helpful to use a screen-capture program (I used Jing and SnagIt) to make grading comments about specific blog posts (because, of course, you should not comment those in on a public blog site).

One last tip:  About halfway to the deadline, I give every student feedback on how they are doing so far.  I gently remind them about details that they might have forgotten so that they have time to correct or regroup.  I’ve found this results in immediate improvement in the blogs and is well worth the effort.  I use quick 1-3 minute Jing videos to give the feedback most of the time.

Note: You can see the rest of the learning projects and a “big picture” idea of how I fit all this in (timewise) by reading Transforming Math for Elementary Ed.