I've been reading some of what Neil Clarke has written about submitting to Clarkesworld. There's a whole lot of interesting stuff, but I liked this in particular (source):
I'll be keeping that.
When I accept a story from someone, I go back and read their previous submissions, primarily to make sure I hadn't missed something earlier. What I end up observing is a steady improvement from one story to the next.
In looking over our submissions data, I've observed that a lot of authors simply give up and give up early: Number of Submissions by Author at Clarkesworld in 2021 – Neil Clarke
Combine those items: Successful authors have enough confidence in their work to keep trying in the face of rejection, but not so much that they think they have nothing to learn, try, or improve upon. It's a delicate and challenging balance to maintain or achieve, but it's the one thing I've seen over and over.
A more concrete suggestion is that they submit to their top markets (everyone will use different criteria for this) first and work their way down. Starting lower than that is the worst kind of rejection, self-rejection. Whatever you think, you don't know what an editor wants. Quite often, they don't know until they see it.
I'll be keeping that.