Y’know the money in your world? The shiny, round things the protagonist usually starts out the novel not having and ends the novel with a lot of?

1) Have some mercenaries who act like mercenaries.

Does anyone else mentally adjust things as one reads? I do it all the time. I quietly alter certain words in lines of poetry so that they scan better, I correct typos in my mind to what they should have been, and I mentally scratch out any mention of “mercenary” in a fantasy novel and replace it with “good-hearted soldier in disguise.”
Come on, mercenaries. Where did all of you go? The wimps are taking your name! Come back and reclaim it!
Oh, wait, maybe they all hid in Glen Cook’s Black Company series. That remains the one saga I’ve seen with mercenaries who, damn it, kept their eyes on the fact that they fought for pay and not for some grand heroic noble ideal. When they appear to switch allegiances, it’s as the result of external ‘do-or-die’ pressure, not because they suddenly grew consciences.
Mercenaries are the greatest victims of authors’ relentless attempts to ‘redeem’ somebody. They’re absolutely sure that most mercenaries are, truly, good-hearted sorts who just act gruff in public, maybe to scare the neighbors. In secret, they’re kind to the heroine and would never, ever think of forcing her into sex or asking her to pay them to fight. They follow the hero out of pure worship, or because they happen to have a blindly stupid tradition of some kind where he defeats their leader and then they owe him their loyalty instead. Forget about surviving on a battlefield! “Real” mercenaries just want to worship the protagonists! (There may be a few exceptions, but they—are you ready for it?—drink, and swear, and say things like, “I like a woman with spirit,” and turn out to be working for the evil guy anyway).
Believe me, some characters won’t see any reason to change. Others will still want money as a guarantee. Others aren’t part of any company, more like freelance thugs, and don’t have any reason to stay with a leader who looks like he’s been gulled into waiting for the money. These are the people who can provide you with minor conflicts, grayed secondary characters, and surely at least one major conflict and a protagonist or two.

2) Put the soldiers’ pay in play.

One of the bits of plotting I’ve most sheerly admired was Guy Gavriel Kay’s use of ordinary soldiers’ pay in The Sarantine Mosaic. The Emperor of Sarantium keeps the money back to build his art projects, including a huge sanctuary (that world’s equivalent of the Hagia Sophia). The main character of the books is a mosaicist, who sees this as a grand project. Quite a few other people agree with him.
The soldiers don’t. The soldiers would like to be paid, thank you, and one of the secondary characters travels all the way to Sarantium to have a word with the Strategos of the armies about what exactly is going on.
This was wonderful because it presented a perspective that just—well, made sense. So many perspectives, motivations, and reasons for being in fantasy books just don’t make sense. They’re not of any practical use to the characters. They might give them something to rhapsodize about, but nothing more. They’re active hindrances to living, and should have been proven wrong by a dozen daily small occurrences.
This was solid, grounded, and rock-hard. Want to do something with your armies? You could do worse than asking where the soldiers’ pay is, and then looking around for a good reason as to why it’s there or not there.

3) Have the characters smuggle something, and react to the smuggling in ways that make sense.

Smuggling! Great concept. Woefully underused. Or rather, it provides the seed of several fantasy plots I’ve seen, but what the writers then do with it makes no sense at all.
First, you have to decide what the ship/person/riverboat (rivers are underused fantasy settings)/caravan is smuggling. When you’ve decided it, you have to decide several things, including: Why is this commodity forbidden? What makes it worth the risk to smuggle anyway? How violent will the reprisals be if the governments on either side of the line find the smugglers out?
“Oh, that’s simple!” says the beginning fantasy author. She chooses hunting dogs.
Hunting dogs.
Right. Why?
“Because they’re valuable, and the smugglers get lots of money for them, and the governments would sooo kill them if they knew!”
Look, beginning fantasy author. You can’t get away with just telling us this commodity is valuable. That’s the first hurdle that tends to trip these kinds of plots up: someone decides that a stone or metal or animal or type of wood or whatever is valuable, and that’s it. Sometimes this will be self-evident, as in when the smuggler is transporting gold or jewels. But what makes these particular hunting dogs so valuable? Are they faster, smarter, keener of sight, capable of magic to bring down their prey? What?
Second, there’s the difficulties of transportation. With live animals, such as the aforementioned hunting dogs, you have to keep them fed, watered, and quiet. The officials will probably notice if the smuggler’s cart of straw starts barking. Also, they will notice if the smugglers are taking food and water to empty carts in a small encampment, or walking away with the local equivalent of the Pooper-Scooper full of shit. They may insist on weighing carts, bales, or whatever other clever contrivance the smugglers come up with, to determine if there’s extra weight in secret compartments. They’ll be sure to do simple things like poke through straw, shift conveniently messy bales around, or look under a thin tarp
At least, they would if the authors tried to get the third thing to make sense. If smuggling is a problem and the government in this port city or across the border the smuggler is trying to cross is vigilant against it, why are the government officials so damn stupid? They should at least search, not “wave the cart vaguely on with a glazed look in their eyes.”
All these things have to work together. Smuggling could provide the cornerstone of a fine plot—no one’s going to question that a pirate character could be motivated by greed—but not when the author childishly removes all the obstacles.

4) Exposing hidden economic motivations can tip a whole edifice of truth and light on its head.

The majority of wars in human history have tended to have economic motivations. Why more don’t in fantasy is anybody’s guess. The majority of wars in fantasy seem to be a) good people vs. evil people, with the good ones, of course, fighting a “just war”: b) races to possess some magical artifact, with no mention of why sending a stealthy thief wouldn’t work instead: or c) “good” wars of conquest where an empire expands and everyone sings its praise.
I’ve never understood the temptation to write positively about empires, myself. The horrific human cost of historical empires tends to sit on my shoulder and stick in my craw rather. I’m much more interested in what happens after an empire gets there, or about what other reasons fantasy monarchies, empires, oligarchies, and so on have for fighting a war.
Say the empire expands to include another country. They promise to let these people retain their own religion, speak their own language, and only send a tenth of their children to fight in the empire’s wars (gee, how generous). In return, they just want access to the mines in the hills and a promise from the countryfolk never to disturb them…
Right away you have the shoots of a novel far more complicated, exciting, and entertaining than yet another paean to an emperor because that emperor happens to be the protagonist, or yet another attack from a “great, ancient evil” that you know will lose in the end. What is the empire doing there? What does it want? What will the people in the country do when they find out? What will the reader do when the empire’s rhetoric of justice and liberation is shown up for the lie that it is? When rebels rise, as they probably will, what complications and further problems with their nascent movement cause? (Use a great setup like this to write Just Another Fantasy Novel about the persecuted rebels and how everything will be all right once the rebel hero becomes king or emperor, and I will bite you).
So much to play with. And all because some people wanted money.

5) Characters who make a living from selling things have a right to care about the money they make.

Or, in defense of middle-class people, merchants, and small shopkeepers:
I’m so fucking sick and tired of seeing these characters portrayed as evil and irredeemable when they want, say, the heroine to pay up a debt that she accrued in the shop over a year of buying food on credit. Why shouldn’t they want that? It’s a perfectly reasonable thing to want. Hell, a year is more time than a shopkeeper in most places would probably be willing to offer. He’s showed his compassion. Now she needs to show the money.
“But the heroine is poor and has ten children!” runs the usual line. And? She might have been desperate, but if she’s as clever and compassionate as she’s usually portrayed, then she’ll have foreseen this and realize the shopkeeper has little choice but to demand his money. She won’t hate him for it, either, not if she’s truly a human being who “sees good in everybody.” She’ll try to find some means of paying up. If she were truly as conscientious and responsible as she’s often portrayed, then she’ll probably have started paying him back before this.
I’m also fucking sick and tired of seeing every person who cares about money at all, unless they’re a happy-go-lucky thief who “steals for the sport of it,” portrayed as a miser or a fop. Really. What is wrong with enjoying luxury? The heroine sure does, once she discovers that she’s actually the daughter of Obscure Royal Line [Insert Name Here] and gets whisked off to the silken sheets and golden plate. Somehow, the princess who’s the heroine of the story isn’t decadent or living off peasants’ blood money if she likes her jewels, even though everyone around her is.
The root of the problem is, as it almost always is, authors turning everyone but the main character(s) of their stories into shadows, insisting that all rules will bend for those heroes and that normal human motivations, compared to their high and pure and lofty ones, are OMG EVIL!!!! Remember: The rest of the people in the story have a right to not give a damn about your heroine, unless you show that she’s actually (not just because you told us she is) a person they deserves to be given a damn about.
Why don’t more people use plain ol’ desire for money, really? Almost everyone feels it in our world, most people are aware of it, and most people would really like to have more money. Yet it gets demonized in fantasy.