This step is more for someone who does online writing/blogging as their side business. For bloggers, a content calendar is a godsend and is something you should be doing every month (in my opinion.) If you run a small business or online store, calendars can help you complete priority tasks, keep up with email marketing and social promotions. Even if you don't blog, you need to have some type of calendar for all of the marketing activity you're doing to, well, market your business.
I created an “Every Day I’m Hustling” shirt and sold enough for the campaign to ship, but didn’t earn much on the experiment because of some not-very-effective Facebook advertising. Still, some opportunity here and a friend of mine is doing REALLY well with this. If you can create awesome designs and reach the right people with good Facebook targeting, Teespring can be very profitable.