This might not be one of the most useful exploits, but it's an exploit nontheless, which has helped me a bit. As a newly dinged paladin in crappy gear.
As most paladins know, Beacon of light is quite expensive to cast.
But here's a little trick. When you sit down and drink, you can cast the spell without interrupting the drinking.
This means that you may cast Beacon of Light on the tank/whatever as they charge in to kill a boss, when you remain sitting and drinking, to regain that mana.
Cast a Sacred shield, a holy light for lights grace, begin drinking and cash Beacon of Light when you're almost at 100%.
In the end, you'll have:
Sacred Shield and
Beacon of light on the tank
and you'll have your next Holy Light cast time reduced by 0.5 Seconds.
And still be at 100% mana.