The exact way you intimidate would be flavored by your God and character backstory but modes of intimidation (verbal, somatic) are usually saying threatening things and making threatening gestures. If you do not want to do tbese circumstantially or on-the-fly then a list of standard intimidation actions like this might appease your GM:
Gestures:
Glowers at enemy
Points at enemy and slices finger across own throat
Martial display (twirls sword, bashes shield, etc)
Points at enemy and grounds heel into ground
Points and makes two handed breaking motion
Thrusts holy symbol at enemy
Verbal:
Commends enemy's soul to god
Proclaims enemy as chosen as a sacrifice for god
Encourages enemy to make his peace in his final moments of life
Tells enemy he will make a good undead servant
Snarls, shouts, wails or maniacal laughter
Tells enemy he will bar his soul from leaving this plane
There are zillions more, but the key for a priest would seem to be to use his holy status against the supersticious nature of his enemy. If the enemy is not superstitious or religious then standard fighter taunts are even more plentiful.
Storyengine has the right approach.
A lot of it has to do with who you're trying to intimidate. An animal will probably only understand body language, tone of voice, and volume. Smaller creatures may be afraid of posturing, while larger ones may be taken aback by a show of confidence or lack of fear in their presence. More intelligent creatures might be shocked by displays of barbarism and bloodlust, or something more clever or witty.
Demoralizing doesn't have to be about fear, either: it can be about humiliation, causing doubt, or confusion, too. Basically, anything that puts them off their game.
You don't always have to aim the insults or threats at the character you're trying to demoralize, either. Non-evil creatures may also take offense to you picking on a vulnerable or conspicuous member of their team, such as a leader, a caster, a smaller character, an injured or dead/dying ally, or so on.
Man, I feel dirty just writing that. lol
Doing the schoolyard bully "Jerk towards them like you're gonna attack and growl menacingly" thing works just fine as a standard.
Movie quotes are good sometimes. Don't go for the obvious ones; they lose their impact if everyone at the table has heard them a hundred times.
I always liked Avatar's line from Wizards, "I've got stuff planned for you that'll take 20 years to kill ya, and you'll be screamin' for mercy in the first five seconds!"
