Grab the reader
Journalists don't like having to come up with their own headline, so come up with something that makes it easy for them. Avoid clichés; try to use a phrase that's new and makes the reader stop and take notice.
Know your market
It's no use speaking in jargon if you're wanting to attract individual consumers. Likewise, businesses don't like being spoken to informally. Set the tone at the start and keep it up throughout.
Structure is key
News sites will generally only want a press release that is correctly laid out. It usually follows a set format, so stick to this. Make sure you stick in all the correct contact info and have a relevant title.
Captivate the audience – don't veer off talking about other products, services, events, charity deals etc – stick to the point. Keep to the topic and constantly reinforce.
Providing a photograph for news sites and journalists to use is a real bonus. Sourcing pictures and paying for them is the bane of every content editor's life – make it easy for them. If your CEO is commenting, stick a picture of him on the press release. A company logo is also good.