You can do this for both normal PQ's and Keeps.
Stay on your mount for the entire PQ, until the very last phase (or keep lord). On the last phase, hit the HERO mob ONLY with as much dps as possible, or, if you are a healer, heal the highest DPS person that is taking damage during the phase. If you are in a keep, focus only on the keep lord.
If you do it properly, you will be guaranteed at least top 3 contribution.