threat generation and spell rotations Follow

There could be a number of reasons you're having trouble holding aggro so more information would be nice, as would a link to your armoury profile so we could see your gear.

That said, the basic pallytanking order of business is:
Put up Righteous Fury
Seal of Righteousness (some use Seal of Vengeance, I personally don't use it except on certain fights)
Pull mobs with Avenger's Shield
Consecrate
Holy shield
Judge as the mobs are in range and reseal, repeating til everything is dead.

Obviously this order is somewhat mutable depending on circumstances and playing style. Your gear also factors into the equation - for example, if you have no spell damage, you will have trouble holding aggro. Then you have things like dps who unload as soon as you've pulled with no regard to aggro, but that's another conversation altogether...

Today is patch day, but that still won't change your basic rotations much, although it will significantly increase your spelldamage if you respec correctly tonight. You shouldn't have ANY trouble keeping threat with all of the increased threat generation you will have.

The biggest problem is PROBABLY DPS related as follows:

You need to mark targets for proper kill order and crowd control. Skull your first target, X your second target, Moon for mage to sheep, Diamond for rogue to sap... whatever you/your group decide on. That way the dps is focusing on the target THAT YOU ALREADY HAVE MAXIMUM THREAT ON.

ALSO, you need to throw your shield, consecrate, AND THE TARGETS (the ones you are not trying to CC anyway) NEED TO GET INTO YOUR CONSECRATE CLOUD BEFORE THE DPS STARTS IN!

If the hunter starts shooting before the mobs hit your consecrate radius, or the mage starts pyro-ing, those mobs are never gonna hit your consecrate radius, they are just going to run to the hunter or mage and mash them into pulpy bits on the floor.

So, basically, you need more than just proper initial threat generation and spell rotation. You also need properly marked targets and DPS that is patient enough to wait until your CC targets are CC'd and your kill targets are in your consecrate before they start killing anything. They also need to FOLLOW the assigned kill order.

If ALL of that goes according to plan, the targets should be stuck to you like glue, especially after the patch today.

One final note, with the changes to Seal of Vengence in today's patch, it is even better at threat generation than it was before, though Seal of Righteousness still isn't going to be bad either. Probably still going to use SoR on trash and SoV on bosses for the most part, though I have to mess around with both before I make a final decision on that.