It falls into three major categories:
- Publishing Credentials
- Professional Career
- Personal Details
Of course, agent tastes differ. Some agents tell you not to put anything if you don't have any good credits. But all the advice I've read says you should put things relevant to your book. So if you're an astronaut writing books about astronauts, it might be good to include that.
For example, Patricia Wood, author of Lottery, writes about a mentally challenged character who wins the lottery. She is a P.h.D candidate studying education and disability, and her father won the Washington State Lottery, so I'm sure those experiences helped her write the book and might have helped sell her query on the novel. My book review of Lottery appears earlier on the blog.
Don't include all regional contest wins - focus on awards with national reputations unless you won the award at a conference the agent/editor attended.
But most of all - you must send out your query. After you've done your homework and refined it, set it free. It doesn't matter what credits you have if no one ever sees your letter.