Once you've targeted your market correctly, and your query has received the go-ahead from an editor, proceed writing your article quickly, while the editor still remembers agreeing to read it. And, if you've promised to deliver the article by a certain date, make certain you meet your own deadline.
Don't procrastinate. We writers can think of hundreds of reasons not to sit down and write. The kids need attention; there's a good show on t.v.; there's a meeting to attend; it's too nice to be inside writing. Stop making excuses and make the time to write. The other things need to happen, too, but while you're doing them look for stories and articles. Keep your senses open and your notebook handy. Jot down ideas. Then, make time to write, even if it means getting up an hour earlier or staying up an hour later.
Check the guidelines for quantity. How many words does your prospective market need? Tailor your article to fit those requirements. You may think you're special and can get away from following the guidelines, but editors don't. No special rules for you. Follow the guidelines and keep your word count within those established by the editor.