Write a query letter. The query letter is your introduction your first impression your sales pitch your marketing tool. So make it good. On your letterhead, include the date, a brief synopsis of the article, your qualifications for writing it and your writing credits. Try to keep it to one page.
Many editors accept queries via email now.
Learn to play the waiting game. Postal anxiety is common among writers as most of us have an ongoing love affair with our mailboxes. Do the research and interviews for the article. Once you get the go-ahead to write the article, line up your resources. Start a file of articles on topics of interest to you.