Wait Until They Bite
I think of PR like fishing; there's a sea full of reporters and editors, and our job is to cast out a fancy line (or in this case pitch them a story) in hopes of them biting. When fishing, you want to make sure not to give out too much bait and be patient with things.
You'll want to apply these same principles to your pitch - don't give out too much information on inital contact. Going along with rule #1, keep everything short and to the point so that you don't dilute the email with fluff. Offer a press kit or press release upon request; if the reader is interested, they'll ask for more information.
*I'm not trying to degrade writers in any way, just using this as an allegory.
I'll leave you with a basic example of how a pitch should look using the above principles. Is there something I'm missing? I'd love to hear your tips!