Most magazines require a cover letter be submitted along with your manuscript. Also, if you plan on submitting an article that you would like accepted for publication, submit pictures you've taken as well. This is definitely increase your chances of being selected for publication.

Make sure the article you submit fits their style of writing and what they're currently publishing.

Have more than one person proof your manuscript before submission. Chances are the editors will select your piece with flawed writing and ask you to rewrite it, but you're better off saving them the hassle and just getting it right the first time.