How do you do a press release?

In a given sector (makers of instruments used in medical procedures in my case), how do you do a press release? And who to? Do you make it only to 'the press' i.e. trade magazines, or to companies in that sector too? How do you find trade magazines and so on?

From my knowledge:

1. You may want to find a copywriter to write your copy.
2. Submit it to a pr service for distribution. Usually costs more money for print release.
3. The newswire may approve or deny the news release based on it's editorial content.

Here are some services that I've used:

• PR Newswire: http://www.prnewswire.com/
• PR Web: http://www.prweb.com/