Here's what I've used in the past.
It allows connections for certain ports/places and then drops everything
else as the last item.
http://linux.duke.edu/~skvidal/misc/iptables-template
it's pretty painless, really.
If we want to add explicit outbound rules, too, that's fine, but I'd
advise enabling logging b/c that stuff is easy to get wrong. :)
This is just a sample but it's simple and straightforward.
-sv