Notice Exorcism is not in it.. Your gonna want to use your instant cast with flash of light not Exorcism unless Exorcism will get them to where Hammer of Wrath is usable. You will also want to start the macro right b4 an encounter because the first cast is Sacred Shield you want that up at all times before you start taking damage! This macro will do pretty well. I have noticed it does not work as well as me.. But It will definatly show you what is needed in pvp encounters..
I have been toying with the different suggested Ret pvp specs online that people have been talking about and have spawned my own for my game play. The pvp spec I use is 7(holy)8(Protection)(56 Ret) Mind you this my toon is fully pvp geared with a little over 1200 ressillence. No enchants or gems with res on it.. You cannot stack res chants/gems and be competitve.. Most of your encounters in arena they are gonna have atleast decent gear so your crits are difficult to land.

* More Macros can be found here
http://www.wowwiki.com/Useful_macros_for_paladins
Just because they are posted dont mean you cant tweek them a tad and make them better…

Until you get to the 1100 mark of ressillence you will need to spec down in the prot tree to pick up Improved Righteous Fury, Toughness 5/5. It will help your survivabilty alot! I cant stress enough Once you dont need those as much you should up your dmg talents asap. It can be the difference in getting that tree down during a stun and winning a arena match. The only classes your gonna have trouble with is a holy pally and a Frost Mage (But they must be pro and know there class and be able to perform)

** Most important:
Bubble,Lay on Hands and Pvp trink usage….

Bubble only if your below 20% and DO NOT continue to fight during your bubble unless your opp is below 20% hp, HEAL YOUR SELF completly for round 2. If your dotted up and feared thats also a good time to pop your bubble but you cant waste time you should do it before the dots take there toll on your hp.. You must also get back to the target and do a better job of staying behind #1 and dps-n#2.
**Use your pvp trink for fears primarly and if nobody can fear you stuns. If someone has you stunned and you pop your pvp trink be spamming Hammer of Justice on them right after you come out of stun! ALWAYS stay behind the attacked! most classes have zero attacks for targets behind them! So why take damage when you don’t have to.. Another words DON’T BE A NOOB!
*Lay on Hands
Honestly I never use this on my self in arena, always my partners in crime if my 2 min cd isnt still ticking.. The only time i use it on myself is if I have already popped my bubble and my 2 min cd from that is over and im less than half health or im taking on 2 at a time and im at 50% hp

* One last thing….
Your specs will change with your gear… Once you grab some decent pvp gear you can consentrait more on your damage instead of survivabilty. You have to give to get right? And if your a Blood Elf Pally your OP! Hammer of Justice followed by Arcane Torrent once Hammer times out is 5 Seconds a caster has to take it like a man. Thats not even counting SOJ/JOJ and a rogue thought they could stun. BAH! Takes some practice, but keep poking you learn, the more times you get owned the more you learn… Oh and the Specs others have discussed are good ones as well, they just aren’t my playing style.. I like to do the damage not heal threw it…

I hope my knowledge of PVP Ret has been helpfull. I still learn new little tricks everyday for certian classes. But a ret pally spells are so situational once you get good at making instant decisions you will be unstopable! And also represent the most OP class in WOTLK atm!