I'll be sharing it as an insta-feed over the next few days, but thought I'd add a little more detail over here.
No.1. What do you want to sell? Sticking to a theme helps to build a brand identity, so creating a ‘collection’ is a good idea. Having a body of work that relates to each other makes it easier for people to understand what you’re offering.
This is something that can develop over time, so don't be scared that you're committing to writing granny square patterns, or making hats for the rest of your life, but do be sure that it's something that will hold your interest at least for a while.
What is your time worth? To be blunt, you will always struggle to make money by selling a finished product. If you are going to, be realistic. Research what similar things sell for, and at the very least make sure you cover your costs. Ideally though, if you're really looking to do this to make money, you need to treat yourself as a business. Work out what you would charge someone per hour for your time. You have a skill that they don't and you should value that.
A more profitable way to do it is by selling patterns and supplies. For me this is much more fun than making the same thing over and over again! It's also much less of an outlay as once you've written a pattern you can either keep relisting it in your store, or offer it to magazines. They can pay between £40-80 per pattern, and you keep the rights to the design, so can sell it in your store again in a years time.