Before embarking on a public relations campaign, the biggest tip I can give you is to define what you want to accomplish. I've listed a number of ways and reasons companies use public relations. Many of the examples are Silicon Valley companies so if you don't understand the example, I apologize, but I think you'll get the idea regardless of the exact example.
Build Product Sector Recognition
The "Got Milk?" television commercials didn't pitch a brand or company name just a general food group. All brands of milk capitalized on the campaign.`
Build Name Recognition
"Of Course, we checked it on our Tencors". Check out how many companies own a Tencor now.
Southwest Airlines has built an identity as a no frills, on time, have a little fun, short hop, no meals airlines through both advertising and public relations.
The most famous one: We're Avis, We Try Harder. (Because we're position #2, not #1).
Pontiac, once known as a Buick clone, now claims, "we build excitement," meaning we're powerful, fun machines. Oldsmobile tried the same thing when they claimed, "we're not your grandfather's Oldsmobile." Yes, you are, because the campaign failed. The car is no longer in production. Maybe it was the name.
Beatrice ran a whole campaign to let you know how many food products they make. BASF is running a campaign now, "we don't make it, we make it better."
Examples: "4 out of 5 doctors recommend."
Counter Bad News
Remember when Tylenol had to be pulled from all the shelves. The PR campaign that McNeil ran calmed the public. Now Tylenol is more popular than ever.
Report Good News
Quarterly financial reports (if they're good) or large sales orders won are two example of good news.
First Kodak, then KTI, then Olin (OCG), then Arch Chemicals, now Fuji Hunt sponsors INTERFACE, The Microlithography Seminar, every year to educate photolithography engineers. Sure it's education and it's great PR, too.
New products announcements, new hires, ISO 9000 certifications, company expansions, etc. (TV ads are often used as examples because they are visually memorable and repeated over and over again.)