I'm a long way from being an expert at PvP but these are some thoughts based on my recent experiences in AV.
1. If you're running away and manage to stealth don't keep running the same direction, take an immediate 90 degree turn and hide. Whoever is chasing you will likely run straight past in the direction you were heading. Keeping on the same heading you were on before stealthing = BAD kitty, no catnip for you.
2. Drinking squishies look so tempting and juicy, pounce is still your friend though. Ravage+shred+FB may come off well with luck and a sleeping target but the usual result is dead kitty unless you have INSANE (i.e. AQ+ raid level) DPS.
3. Warlocks and rogues are not your friends, travel form is.
4. When healing try not to stand well to the rear, hiding in the middle of a mob makes you less of an obvious target to the nasty rogue types who'd love to ruin your day. In particular, don't stand on top of the hill outside the hall when fighting warmasters in AV, when a horde mage comes to ruin the day of all the healers/mages clustered there you can smile to yourself, root him as he's now OOM, and carry on healing while some kind person finished him off.
5. Going OOM then switching to cat form to melee while regenning mana can be a good move. Not switching out of your healer gear before entering melee combat is less good and can leave you somewhat bemused at your lack of DPS (and incidentally, dead).
6. Warlocks and rogues are REALLY not your friends, seriously.
7. When healing, taking the odd break to hunt through the enemy ranks for almost dead players retreating then dropping moonfire on their heads can be very satisfying.
8. Bear form and swipe can be great for distracting clusters of enemy healers.
9. Unless you specced heavily into balance starfire sucks. I mean REALLY sucks. Sucks like a fifty dollar whore in fact. Like rogues and warlocks, starfire is not your friend.
10. Killing blows mean nothing, winning the battle is all that counts. Individual skirmishes count for zip come totting up time.