Personally I never really had much of a problem against priest, which the strat is very similar to locks (not saying its a full prof system, since our counters aren't exactly "full prof"...but techincally it works".
When you see any priest, first move is usually Tremor totem (same goes for locks)! Keep mindful of the range you wander from where you put that totem down, cuz they WILL fear you, eventually. Unfortunetly, the totem doesn't make you "immune" to fears, it just gives a chance to cure it, and hopefully when they do fear you, for the small bit of feared running you do...hopefully it won't run you out of range of the totem to dispel it....hopefully. Either way, Tremor is the only defense we got against it, thus its still the first move you got.
Next move the priest is going to try and get you with is the Vamp. embrace(touch). This can be earthed shocked, letting this drain you and heal them is not a good thing. Granted even tho we can heal it back, this will start to turn into a endurance match...something that we sham's will always lose, so don't get caught in this trade off.
If you take away their drains and CC, that pretty much leaves them with nothing, except for their attempt to kite you away from your tremor tot (like I said, be mindful of where you are in regards to its range).
Keep in mind, when things start to get ugly for them, they fall back on their bubbles...something we got a answer for too (purge....thus I love taking down priest), which then all they got is cloth after that...and we know thats not going to last long underfire.
If your enh, its pretty easy to just melee them down, assuming you don't get feared away (hopefully the tot covers you here long enough to pound on them), one good WF proc, and that should be lights out! Striping them of their bubble, CC, and their money move...and they don't got much after that. You can use discretion shocking their heals too of course, if they try to fall back on a last ditch effort to live longer, but a good enh sham, should be geared up strong enough to make this a moot point, and drop them b4 this is even a option to them.
Elem sham's have a little more flexibility, in the sense that since they rely on range attacks, that means they don't need to stray far from the tremor tot. Just shock, bolt, purge. Hard part is if they try to run out of range of our shocks to heal up, which could run us out of range of our tot...but thats a gamble your going to have to take. Trick is that sham's have the tools to bring a ton of dmg on its target fast (in either elem or enh)...assuming you got the gear to support it...and your going to need it!
They more than likely will dot you up, granted shadow priest dots aren't as bad as Lock dots, and the confrontation "should" be shorter than the dots duration...or at least thats your goal. If not, this is where NS+HW comes into play. Be warned if it comes down to the "healing" game...thats another form of endurance match...once again..we lose thoughs. Especially if they are stuck in shadow form, their "heal" is that vamp move, thus that needs to be shut down fast. Hopefully, u'll beat them fast enough that their dots don't make things critical for you, which u'll have the freedom to cure/eat out of them, when they are dead.
Things that make this none full proof, is usually the "fear" factor. Yes, they "can" fear you out of range of your protection, and even if ur in its field...doesn't mean that your fearless. Further more, they "might" know that your earth shock has a pretty short range, so they "might" try to kite you away from your tot, knowing this (especialy if they know its what helped you the first time they made the attempt to fear you). At which case you can either case after them, to get in range to shut them up...course thats the gamble that they might try to fear you instead of heal. Watch to see which form they stay in...it could just be a fake to a fear and vamp.