I hope my imput won't be too outdated... Here are 50 tips how to avoid mistakes in a press release. In my opinion it appears to be a very useful article.
Being a PR pro, it's one of my favorite topics to write about. You can find a template, tips, instructions on press release writing, and more at http://blog.bizammo.com (I'm going to try to move the whole collection to the main domain today, so if you don't see a "public relations" section on the left when you check, then just remove "blog" from the domain.).
@jo_cstd and Garkoni, I am pleased you liked the link, guys. Jenn, your second name is Pandora's Box (as once YourContent mentioned) - you link is great for those really appetitious to learn.
Maybe try to write one that you would have liked to read yourself. And dont forget the keywords of course.