Here's a question I was recently asked: What would you consider a medieval cliché?
After much thought and revising (because, as when writing my book, it can take me awhile to get to the heart of the matter), this is how I responded:
Here's the thing that always gives me pause about such a subject: What makes one thing a cliche and another a story element medieval romance readers have come to want and expect? There's no hard line there, I don't think. And I've been in this business long enough to know it's often not the "what" but the "how" that sells a book.
That said, I think a story seems cliched not because of what the writer's done in terms of using plot elements that could also be called tried-and-true, but because he or she hasn't done enough in other ways to make the story feel fresh. Sometimes a writer's voice alone will be enough to make a story seem fresh and different. That's nice if it is, but I don't count on that. I focus on trying to create unique characters with interesting backstories and believable motivations.
For example, take the book I'm writing right now, THE WARLORD'S BRIDE (HQN, January '09). It's an arranged marriage story (been done many times by many authors). The heroine is sent by King John to marry a man she's never seen. However, she doesn't protest or rage (the more cliched response, I think); because of her recent past, she takes a "wait and see" attitude and does what the king orders. When she arrives at her potential groom's castle, the man who comes out of the hall is old and out of shape, but very friendly. She's been told very little about the man the king wants her to marry, so she assumes he's the guy BUT she doesn't think, "Eeeuuww" and run away, or fly into a temper. She thinks, "He's nice, he's friendly, he's probably too old to be ambitious" (in other words, a complete contrast to her first husband, who was handsome, young, ambitious enough to plot treason and extremely cruel), "so I could do worse." She's wrong about the groom BUT when she finds out her husband is young and handsome, she's actually and sincerely disappointed (although she can't deny she'd prefer to make love with him and therein lies some internal conflict).
However, while I may try to avoid a cliched feeling most via characters, I do try to put different twists and turns into the story as well. An author might also use a unique setting, or an obscure historical event, or a combination of some or all of those factors to make a story new and different.
I'm loathe to tell a writer they should *never* do something or use a particular plot element. Too much depends on the individual writer and how he or she uses it.