One of the best threads in SEO is Cre8asite's one on Press Releases for Google News. Advice given there ranges from source to source but is all of very high quality, including an actual illustration of the traffic and readership levels that can be achieved with a successful release.

While I encourage a full reading, I'll pull a few highlights:

From Bill Slawski:
The timing of when you send out a press release can be very important, too. If at all possible, try to send yours out so that it gets submitted into Google news in the morning, rather than the evening, in the area where your largest targeted audience might reside. Chances are very good that it will get many more views that way. Google news can cycle through stories pretty quickly and a lot of people "sort by date".

From Grumpus:
Once you have some content in your News Area, ask Google to include it. Go to the "News Contact" page, select "I'd like to suggest a news source" and fill out the form. Be honest, and mention how frequently you update it, the general topic of your news, and so on. This is the ONLY way I know of to get listed in Google News unless you are syndicated by someone already in there. If you don't tell 'em it's news, they won't know. And make sure you've got some news that they feel will be worthy of indexing. It's rather like getting a DMOZ listing - if the quality isn't there, they won't list you and if you aren't listed, nothing I've written here is worth a halfpenny.

From Eric Ward:
URLwire site announcments are indexed by every major search engne in a day or so, and are also syndicated via moreover's cool sites feed to 10,000+ other sites. Other wire services can't get in that feed because they publish too many releases each day. Can't put 150 announcements into a feed if that feed only publishes a few each day, right? That's why when you are announcing a web site, URLwire will always be one of the two or three services you should use.

From Whitemark:
Tuesdays and Wednesdays are the best days for getting optimized press releases to the top of the pile. And journalists are typically searching for story ideas on those days.