I am aware that the cleric is not a well-loved character class, and that later editions in particular have recreated it into a field medic, the perception being that with more healing there's more killing. Religion in general is not popular with a lot of D&D players (that whole persecution thing is closely felt), and as such the theological aspects of the theological class are downplayed severely.
Still, I think it is a matter of outlook. With that in mind, I offer these suggestions.
Reverend Cleophus James: DO YOU SEE THE LIGHT?
Jake: THE BAND!
Reverend Cleophus James: DO YOU SEE THE LIGHT?
Elwood: What light?
Reverend Cleophus James: HAVE YOU SEEEEN THE LIGHT?
Jake: YES! YES! JESUS H. TAP-DANCING CHRIST... I HAVE SEEN THE LIGHT!
One. Have an agenda.
I don't mean something lame or overdone like "following my god" or "building a church" ... your cleric needs to reach for the stars. Your cleric needs to conceive of some world changing strategy that will shake the pillars of heaven and pull them down, thus establish his or her self as the greatest religious leader of their age. This will require more imagination than being a cog in the existing religious structure; it means, on some level, replacing the religious structure with one that is better. How better? That is for your cleric to decide. It doesn't matter if the goal is nearly impossible ... eventually your cleric will be high enough level to bitch slap those who don't view the world with your cleric's agenda. This is what you must plan for! Conceive of other clerics under your guidance giving instructions to kingdoms and empires on how to behave and give money; conceive of a world-wide entity that is perhaps benevolent, perhaps sadistic, which everyone acknowledges as holding the greatest possible truth about life, the universe and everything.
What, you don't know what this truth is yourself? Well, for heaven's sake, follow in the traditions of thousands of religious leaders who have gone before you and make shit up.
Elwood: They're not gonna catch us. We're on a mission from God.
Two. Know your importance.
If you think religion is about following the dictates of your god, you know nothing about religion. Religion was created for the cleric, not the cleric for the religion. Your God, his or her minions, their powerful agents, the heroes and the priests have your back. They are there to help YOUR agenda along ... remember, you've seen the light. You know what's needed ... and as you go forward, hacking and slashing and pressing forward your religion, the gods will recognize your worth and clear the road for you. Count on it, expect it ... and rail at the heavens when it does not happen, as did Moses, Jesus, Mohammed and all the great ones. Remember, the holy word is conceived in holy writ - which if your cleric is on the ball has carefully taken the time to write down, just to demonstrate to all how the gods speak through you. You might want to get on that, when you can. How do you suppose these holy words came about?
Jake: Ma'am, would it make you feel any better if you knew that what we're asking Matt here to do is a holy thing?
Three. Get your party on board.
This can be difficult, especially since you've recently become an obsessive megalomaniac ... but it can be done by emphasizing how your agenda serves the party's general needs. Seize wealth from the infidels? Check. Crush enemies without hesitation? Check. Perceive the cleric's own church as a collection of misguided fools who have no right or privilege to tell the cleric, or his party, what do to? Check. Give free reign to the party to act as they please, so long as occasionally they mention to the cleric that they may have gone a bit far? Well, that might be difficult to work out, but so long as you, the cleric, show some general pride for the party's general mayhem, couched in the occasional praise met with a hint or two towards contributing to the general welfare (yours), they might gratefully acknowledge they'd all be dead if you weren't there to bring them back from the grave, or speak a word or two to get one of the higher ups to bring these poor 'sinners' back from the grave. You might want to mention that from time to time, to keep it in the forefront of your party's mind, so that while you're indulging their murderous activities, they're indulging your pocketchange. It's a give and take ... and it is up to you to make them understand that. Don't let them push you around. Make it clear that you are there to be needed; and they are there to pay for it.
Jake: Your women. I want to buy your women. The little girl, your daughters ... sell them to me. Sell me your children!
Four. Be ruthless. Be without scruples.
It is a silly cleric who limits his or her own success with a lot of morals which - honestly now - are just ambiguous, inconvenient rules made up by other people who can't understand why the world doesn't work the way they think it does. You, the cleric, you know better. If the agenda is going to require ten thousand female slaves in revealing steel armor, well, then it is. That should not be questioned! It is the agenda! And those who don't understand or don't appreciate the beauty of a thing like that will die under your merciless phishy phalanxes. That is the word, and the word is made flesh ... revealed flesh in this case. Remember that whatever is necessary IS necessary, and that is the end of the discussion. Your cleric will decide what is necessary ... and further, of course, what morals other people are expected to adhere to. That last is obvious.
Elwood: It's 106 miles to Chicago, we got a full take of gas, half a pack of cigarettes, it's dark ... and we're wearing sunglasses.
Jake: Hit it.
Five. Pay attention to details.
Pomp and ceremony is the eye-catching, shiny mollifier that will drive others to be mystified and excited by your presence. It is all public relations ... how you present yourself, how you direct your actions and the order and degree to which you take actions are important. Each morning, you should have included in your agenda habits which you will not break. It is your attention to detail that will make others agog at your preparedness and your diligence. You do not care if the dragon is approaching. It is time to kneel and say thanks, and if the dragon doesn't know that's more important than the dragon's silly agenda, that's too damn bad. Your god has your back, right? Then the damn dragon can wait until YOU'RE ready to meet with him. I cannot stress enough how important this is to your character, his or her nature or the party's reflection on how you have chosen to act. While yes, this should not be an obstacle to the party's temporal needs, it SHOULD be something which everyone is aware of and which everyone respects. Like wearing sunglasses. Like having your pinch of snuff before entering a mysterious cave. Like the thousand and one other momentary pauses you insert into your cleric's day.
The better you can imagine out these five things, the better cleric you will be.