Well I've been playing my cleric for about a week in RvR so here you go: lw, tireless, purge2(minimum), perfect recovery, divine intervention, mastery of arcane, Aug Dex, mastery of the art. Honorable mention to wild healing to introduce the chance to crit heal to your arsenal
I would also add Barrier of Fortitude to the list in the previous post... plan on popping that in 90% of engagements with Mids, because of their melee trains.
While leveling, I would prioritize LW, Tireless, Serenity, MCL, and a point in Wild Healing (for the chance to crit mentioned above).
At 4L2 you should probably have something like: - Longwind - Tireless - Serenity 1 - Wild Healing 1 - MCL 1 - Purge 2 - DI 1 - PR 1 - BoF 1
I think having actives like these are important for two reasons. First, they give you the ability to respond appropriately to different situations in RvR/PvP. Secondly, they allow you to gain practice with using them in those situations. Basically, they help round out your toolkit and help you start building muscle-memory for those skills.
From then on, you can start acquiring passives like Aug Dex, MoArt, and MoArc.
Once you have passives at the point where your casting speed and buffs are where they need to be, you can begin the long road of improving your active RAs.
This is my general strategy, and your mileage may vary. Hope that helps!