obvious answer: draw fuckin'
Unfortunately, that's only good if you can draw. Sales and shit is a bad metric for gauging yourself because anyone will buy anything for any reason. Remember the Jesus toast?
For me to want to read a comic, it has to at least have an interesting story that can be ingested in 1 or 2 parts.
The art isn't a huge sticking point for me (though it helps) if the story is good like in the case of Watchmen, Sandman, or really anything that sticks to the Newspaper style aesthetic that seemed most prevalent before the 90s.
Read acclaimed comics. Figure out why they work. Don't copy the formula, but build your world with it in mind.