Pitching is without a doubt one of the hardest parts of making comics. I think over the years I've gotten better at it, but it still doesn't change the fact that it makes me crazy. It's hard enough trying to write good stories, but selling those stories is a whole other animal. It takes a special writing skill, and patience, loads of it! Here's some tips I've learned over the years, but please feel free to school me as well, because I can always use the help.
First off you want to make sure you have just the right package together. To do that you want to make sure to know what each individual company wants, and even if you know the people you are pitching to it sometimes helps to follow their guidelines. For the most part what they want to see is at least 5 pages of art, a synopsis, and a cover. I tend to feel the more pages the better, but you can easily feel out who you are pitching to with some quick emails.
Second, make sure every word from the synopsis to the letters in the pages are spelled correctly, don't be silly with this. You want to look as professional as you can! And in the same token, make sure your artist is rocking every page, and also that your cover looks compositionally and eye-poppingly perfect!
As for the writing of the pitch itself, which is what I wanted to originally post about, that usually consists of the synopsis and a cover letter of some sort. Sometimes these two things can intermingle into one document. There really isn't any standardized way of doing it, and you might want to try something new each time. I do that, because let's face it not every approach works and I have the rejections to prove that! Some do though, which usually leads to a contract, and let me tell you that is one of the coolest feelings ever! Anyhoo, make sure you have all of the pertinent info in there including what the gist of the story is and how it will progress, what's the catch, how many issues, if you're feeling froggy how to market it, and of course your complete info.
Finally be confident, patient, and don't let rejections get you down. Confidence in first your project, and second in your ability to sell it. Patience in the wait it can take; move onto something new! And the rejections? Well they do suck, but there are plenty of comic companies these days, and more on the horizon. Even if you've gone through the list, you can always self publish; which in itself says a lot about your character and no one will ever take your resolve away from you.
To end what's become a column here, pitching can be frustrating, but it's rewards can be awesome. I sent out two today and every time I do it makes me realize what a scary but completely fascinating part of the job this is. Most importantly I feel like when I write a new pitch I become a little bit better at writing, and that's a real good feeling to have. If I provided any sort of insight you didn't have before then cool, I hope you took something away from this post, and if not it was fun for me to just write about it anyway. And like I said if you have any advice for me feel free to fire away!