Quick and dirty
This type of post is usually a short one about something that is documented elsewhere put you want to point out to your readers. A comment or opinion of your own might be added and you might discuss how it relates to your institution. It also might be more of a behind the scenes topic, perhaps a teaser for an exhibition or activity that is coming up.
Long and clean
This is the type of post where you're creating a lot of original content, or creating a new varition or interpretation of original content, along with some commentary.
Somewhere in between
There are also variants of these two typoes
Wunderkammer
Wunderkammer is german for "Link Dump", and is a term that Seattle museology grad student Lynn Bethke coined about the format of how we do some blogging at the Walker. This type of post is a collection of links to things you or your visitors might be interested in, but are not necessarily worth devoting an entire post to. They work as a great way to fill in the gaps when you're between the meat and potatoes of what your visitors are probably coming to your site for, "long and clean" posts.