This macro is what made the omgwtfcritme for mages famous. It will cast your Arcane power to start, followed by your top most trinket, followed with the presence of mind (POM) and then baaam pyroblast. Good for some instant gibs of lowbies and fast crits for other PvP encounters.
/cast Arcane power /stopcasting /use 13 /cast Presence of mind /stopcasting /cast pyroblast /stopcasting
If your favorite dps trinket is not in the top slot switch it from /use 13 to /use 14 to use the lower trinket.