You're getting some great advice here. Posts #2 and #4 offer the most common and the best advice there is, in my opinion, as to how a person can most effectively develop as a writer.
Growing as a writer effectively boils down to reading and writing with consistency and focus.
You mention that you have trouble fixing work after a first draft. Another piece of advice is to learn to think of editing your work as part of the creative process. Editing is not just part of the writing process, but part of the creative side of what goes into writing a short story, a novel or a play.
As an exericise you might take a story you've written. Save one copy on your computer as version one then be very free in the changes you make to the story and edit with abandon. Cut words. Cut sentences. Cut paragraphs. Look for holes and fill them. Then save this as version two and compare the stories. Ask yourself which one is better.
Usually, it'll be the second version.