I entered this into a Spoonflower competition recently, and thought it would be a good place to start with my new RedBubble account as it was already a repeat pattern. I've only put a few designs up so far, it's quite a time consuming process!
Update about a year later: Here is how my Redbubble shop looks now. I add a new design or two about once a month. If I'm honest I don't really do much self promotion, which is bad, but I still earn about 50 Euros a month, which makes it worth it for me :-) It definitely goes up a little bit every month (it started out at $1.95 in the first month). I hope this helps someone else starting out, don't give up!