The subject should be clear and concise. The first word of the subject should be the kernel type the story refers to (such as Linux, FreeBSD, etc...) followed by a colon, and then the actual subject. This requirement is to help people viewing remote KernelTrap feeds who are only seeing the headlines.
The story itself should include links to relevant information whenever possible. (Not including useful links is one of the main reasons submitted stories don't get published)
If the story is based upon emails from kernel mailing lists, include the full email(s) in the body of the story. In addition (not instead of) to including the full emails, it is useful to provide a link to the thread's first email in an online mail list archive. When including emails, be sure to include who the email is from in bold (From:), which list the email was sent to (To:), the subject of the email (Subject:) and the date it was sent (Date:). Remove all other mail headers.
The best way to learn how to properly format a story is to refer to stories that have already been published.
You may also find the 'ktprep' script useful. It is a short perl script that I (Jeremy) use when preparing stories for publication on KernelTrap. It's not perfect, but it's a good head start...