If you want to take this one step further, actually trying to crash an
application in a reproducible way, or trying to narrow down a bug to a
specific set of actions can be really helpful as well; for instance, if
there's a bug that says something like 'If I run this application, it
sometimes segfaults when I close it', and you can narrow it down to 'if
you run it, and use this and this and that option and /then/ close it,
it will segfault', that's very nice.
You can browse our bug database at <http://bugs.debian.org/>. A good way
to start is to search for any bugs in software you regularly use, and to
see if you can help out.