Here's a worthwhile place to start: http://www.amazon.com/Quick-Dirty-Guide-Freelance-Writing-ebook/dp/B00NT7A6HI/ref=asap_bc?ie=UTF8

I published a bunch of my successful pitches here: https://www.amazon.com/dp/B00NT7A6HI

Seems appropriate to post this here: https://www.amazon.com/dp/B00NT7A6HI

The Quick and Dirty Guide to Freelance writing by Scott Carney, an investigative journalist for Wired. https://www.amazon.com/dp/B00NT7A6HI/ref=nodl_