One of the best ways to improve your writing (other than actually getting a formal education and reading lots and lots of books on craft) is through critiquing.
As a writer it is so hard to distance yourself from your own work. You can edit to your hearts content and still miss things.
Through critiquing, we train our eyes to look for problems. Is there too much passive voice? Are there too many echos? Is there an obvious abuse of the dreaded -ly's? Do we lean on crutch words? Does the dialogue sound too wooden or forced?
I've noticed that after a good session of critiquing, I can return to my own work with a stronger critical eye.
I begin to see the things wrong with my own work and often, while making my notes, notice that I am giving myself the same or similar advice that I gave in my critique of others.
It's not 100% fool proof. I'll still never catch all of my mistakes, but the process helps me get closer to something that will be ready to submit.
And also, let' not forget the other benefit of participating in a critiquing group. What we don't catch ourselves, others will likely catch.