Here's what I've learned from several calendar shoots ---
Do ... contact a printer first to get their specs
Do ... bring a lot of backup equipment
Do ... shoot RAW so you have more colors to work with and more lattitude when you edit the images
Do ... get paid for all your time, preferably in advanced.
Do ... scout locations in advanced
Do ... tell models to arrive an hour or two in advance of when you really need them
Do ... hire an assistant. Even if you've never work with an assistant on a shoot, a good assistant can help speed things up and allow you to spend some quality with the client.
Don't ... take a percentage over payment. Most calendars (those without a big corporate sponsor) don't make money.
Don't ... think that all the models will actually show up. Bring backup models.
Don't ... think you can shoot more than a few models in a day (and do it right)
Don.t ... forget to HAVE FUN!
Just my opinion.