Okay so, I'll take a swing at providing something of an outline for Clerical PvP tactics.
As a Cleric we have many tools at our disposal, the most important key (in my opinion) is knowing your abilities and how they abilities work and in what situations they work best.
1) Buffs - As Clerics, we have a great suite of buffing spells and abilities to use.
A) Spells - MPP, PFE(if you'll be using FoU), MaPP, and Bene are a great quartet. Throw in a MaF if you decided to learn it and you're pretty set on durationals. Additionally, learn to use your OM. SoL and Centering are basically OM staples of most any Cleric. For PvP, you'll want to throw in Halo and CoE.
B) Communes - Eluned's defense commune is your friend. Use it. Additionally, Tamsine's offensive commune is a pretty sizeable bonus(presently) for using mundane attacks. Hodierna's staunching commune is also situationally useful (though moreso for invasion/gmpc fighting scenarios).
2) De-Buffs - As Clerics, we also have an amazing suite of curse spells for practically any situation.
Your opponent parries (or hits too hard!) or blocks too much? Throw a CoZ on them to make their weapons and armor like paper!
Your opponent is a little too tough to hit or is making a little too much contact on you? Throw a Malediction against their defense, offense, or both!
Your opponent keeps casting bad juju at you? Throw a Hulp on them!
I'm sure there's more I'm leaving out that covers other situations. This is just an introductory outline. If you have further questions, please do not hesitate to post with any questions or send me an IM (liuridr on AIM) or PM me here as well.
~Regards,
Liurilias