"Work through the PR database".
Prompted by Doug <Doug@gorean.org>, who in an e-mail to an interested
contributor in -hackers wrote;
On Sun, Jul 18, 1999 at 12:01:43PM -0700, Doug wrote:
[...]
> Step three, (and I can't believe this isn't mentioned in the handbook) if
> there isn't anything on that page that looks interesting to you, take a
> look at http://www.freebsd.org/cgi/query-pr-summary.cgi and see if
> anything there strikes your fancy. Look first at unsassigned PR's, but
> if one of them that is assigned to someone looks like something you can
> handle and have time to work on, mail the person it's assigned to and
> ask them about it.
[...]
So now it is mentioned in the Handbook :-)