Starting off small
You're new to this, looking to slowly ease your way into using the Light to amuse yourself at the expense of others. We've all been there, young one -- here are a couple tricks you can pull that are both easy and humorous.
Cast Blessing of Kings, then immediately cast Blessing of Might to continually erase Legacy of the Emperor/Mark of the Wild. This one used to be a lot of fun when these spells cost reagents, because you could plan ahead and make the druid unwittingly burn through all of his Wild Spineleaf while you're sitting on a stockpile of Symbols of Kings.
Use Hand of Protection to prevent players from dealing physical damage. Not only does this work for your typical melee classes and specs (rogues, warriors, death knights, monks, enhancement shaman, feral druids, and other ret paladins), but it works for hunters as well!
BoP can also be used as friendly fire in PvP, particularly when dealing with flag captures. See a rogue capping Gold Mine in Arathi Basin, but you're trying to go for Arathi Basin All-Star? Toss BoP on him and he'll lose his progress on capping the base!
Moving on up
Eventually you grow complacent and bored with such simple tasks as fighting buff wars or throwing BoP on your Recount competition. There's a new smell in the air, and while you're not sure exactly where it came from, you know deep within that it has always been lingering. It's the smell of unspilt blood, a stench that is beginning to dig into your brain. Surely, something must be done.
Cleave your fellow melee through the clever use of bubble-taunting. One great example is the trash immediately before Elegon, the Mogu'shan Wardens that have a large frontal cone attack called Forceful Swing. If you time it just so, you'll be able to see your friends go up, up, and away while you remain firmly rooted thanks to Divine Shield.
And yes, because Forceful Swing is physical damage, you can prevent yourself (or others) from being flung by casting BoP on them, which makes lining up for the And... It's Good! achievement all sorts of fun.
Spread debuffs throughout your group, using your Light-given defensive abilities to keep yourself alive. That's right, you can be your very own Typhoid Mary, or Mark, whatever the case may be. A few recent applicable spells that come to mind are Wildfire Spark on Feng, Visions of Demise on Empress, and Lightning Prison on Protectors.
In the big leagues
You've had your fun injuring your allies and infecting your friends, but even that isn't satisfying you anymore. You ache for a worthy challenge, for a betrayal so spectacular that the urge for retaliation is wholly supplanted by sheer awe of your achievement. Luckily, a couple things come to mind.
Buff yourself with Righteous Fury while DPSing. This one may seem simple, but in order to truly pull this stunt off you have to not blow past your tank's threat, thereby making it obvious you are up to no good. Ride the tank's threat, occasionally pulling aggro and forcing a taunt. Keep the tank on his or her toes this way for an entire encounter, and when you hear them exasperatedly exclaim their frustrations after the fight is over, you will know you have succeeded.
Break a target out of crowd control, then immediately use Hand of Salvation on yourself. This will force the target to chase after their controller, and puzzle the would-be incapacitator to no end. Make sure to turn Seal of Truth off, as you don't want Censure to tick after Salv has worn off (nor do you want an abundance of evidence of your guilt).
Naturally, this isn't an exhaustive list of misdeeds an enterprising paladin can perform. When was the last time you succumbed to the darkness?
The Light and How to Swing It teaches you the ins and outs of retribution paladins, from Ret 101 and how to gem, enchant and reforge your retadin, to essential ret pally addons.