No trying to be objective about this. I'm still going to try to suggest fixes for the problems I see with these, but I wish they would go away far more than I wish that people would just use them better.
1) For the love of whatever deity you believe in, make your prophecy short, obscure, and not automatically pointing out the hero. To return to the Bad Example Book of the moment, The Wayfarer Redemption: Here we have a prophecy that tells us exactly who to cheer for, reveals many key events, and goes on for a page and a freaking half.
No no no.
Your heroes should have something that makes them cheer-worthy outside being Chosen (see below). Having a long and clear prophecy destroys all the suspense, since rare indeed are the authors who introduce the idea that destiny could be wrong. Most of all, I feel when I read a prophecy like this that I'm being forced into agreeing that of course everything in the prophecy needs to happen, when I'm much happier figuring that out on my own.
Nothing like a prophecy to try and excuse lazy plotting and bad coincidences (oh boy, am I ever talking to you, Robert Jordan and Terry Goodkind).
2) Make your heroes heroes because they are, not because destiny says so. Another Bad Example Book: Anne Bishop's Black Jewels Trilogy. Long before the savior, Jaenelle, does anything heroic, the other characters are mooning over her because she's the Chosen One, Witch.
If you listen hard enough, you can hear me screaming.
I don't want to be told that I should cheer for someone just because a crappy piece of poetry recited a few hundred years ago refers to her. I don't like being told that of course this twelve-year-old would make the best queen, just because she has the right blood flowing in her veins and the right set of genitals and destiny hanging all over her.
In other words: Show us characters who could reasonably assume the throne even if destriny wasn't present. If others stare at them in stricken awe just because of the prophecy, you're trying to use destiny to excuse character development again.
3) Consider what the consequences of the prophecy say about destiny's philosophy. Yet Another Bad Example Book: Lynn Flewelling's The Bone Doll's Twin. The land has suffered under a mad queen, and when she dies, it suffers again even though her son is sane, becuase only a woman can inherit the throne.
So having a woman on the throne is more important than having a sane ruler, even if he's male? What a nice philosophy. That book frustrated the shit out of me because of the characters nodding and mouthing about prophecies, and caring for the hidden monarch, Tobin, to the point of being willing to create a sacrificial lamb just so she wouldn't be lonely, the poor widdle thing.
If nobody matters next to your monarch...
If it's somehow all right that everyone suffers for generations until the 'right' person comes along...
If otherwise good rulers are disqualified just because they don't have the right blood or the right crappy piece of poetry...
Think what that says about Destiny. The forces of good are going to come off looking sadistic. "Suffering is fine, as long as The Prophecy is fulfilled!"
Pardon me while I cheer for the bad guys, who are at least fighting this sadistic force.
4) Don't automatically punish the irreverent characters. So many times, those who scoff at prophecies in fantasy are shown as being simply stupid, which is stupid in and of itself. Who in the world would have a reason to believe this old man and teenager turning up on their doorstep and claiming to be the saviors of the world? A little doubt is at least normal.
But most characters are never allowed that doubt. The old man or woman shuts them up immediately, and the child proceeds to be "special" in some stupid way, and the doubting character is silenced.
To turn to a Good Example: Storm Constantine's Sea Dragon Heir, which I'm reading at the moment, has the main character being amused when she first learns of her hidden heritage, and thinking all these piously mouthing women are a bit weird. She does change her mind, but she was allowed that moment of doubt, and she is also allowed to touch the Not Nice side of the powers her people once worshipped, which makes this book so different from any others I've read recently that you could listen hard and hear my shrieks of relief.
5) No royal heirs raised as peasants. This is the plotline I hate most in all the world. It should be tied out in the desert, covered with honey, and left for ants to find.
How do I hate it? Let me count the ways:
a) Used by every author from here to beyond, and I think I've read only two books that convinced me it could work.
b) It insinuates that no one of peasant stock could actually do things on his or her own, that the royal blood is the "reason" for the heroic deeds. Way to turn back the clock and clout down independence.
c) How in the world would someone who had grown up in a sheltered village all her life be prepared for the complexities of politics and ruling a nation? Usually, the fantasy journey is supposed to teach her that, but I have yet to see a fantasy journey that does. It's all about "growing inside yourself" and "fleeing from enemies" and "finding the Quest Object."
Excuse me, but how do any of those make a good monarch?
d) It's used as an excuse for angst. "Waaah! I am adopted! Waaah! I am deprived of my heritage! Waaah! How evil the usurper is..."
And then Limyaael smothers the whiny royal heir with a blanket.
e) It makes the evil people look damned incompetent. What, they managed to kill all the other members of the royal line but somehow missed this one?
I want this plotline dead, dead, dead. Stupid-ass thing.
6) Consider having something go wrong. Another problem with the destiny plotline, especially in amateur fantasy fiction, is how few losses the destined character actually suffers. Yes, she could have her magic go out of control or her family die, but have you noticed how rarely that actually happens? Her family turns out to be alive, she gets the training in time to control her magic, and she takes the throne, la-da-dee-dee-DIE-DIE.
Some authors go the other way (Lynn Flewelling, again), and have EVERYTHING bad happen to the destined character. This makes the character look passive, and smacks of author manipulation. "But, oh look, she suffers! You must feel sorry for her now!"
Sorry, I don't. I just want to smack the whiner and tell her to grow up and get a life.
As always, if you must use destiny, try to avoid the extremes. The character shouldn't have a charmed life, but neither should she sit around uselessly and get angst dumped on her.
There's a reason that in the parodic fantasy series I write, prophecies are completely wrong a lot of the time, whiny royal heirs are seen as the young stupid people they are, and Destiny is a moronic force most of the time.
Hate these clichés. Hate them.