I'd say one of the most important 'must do' things is understanding the audience your comic is for.
Really, your comic is a product, and before you even get to storyboarding, writing, or even sketching, you'll need to know who this is aimed at. Once you figure that out, everything else will flow together much more cohesively; your comic, your engagement with the fans, your marketing, etc.
I see a lot of creators trying to appeal to mass audiences by introducing many elements and tropes to their stories but this can really spread the material thin. No one comic will please any large number of people, so it's much better to just focus on your target audience. They may be smaller in number but they will be more passionate about your product. In time, that small base will grow because the quality of your content remains.