This is meant to apply to teachers and trainers as well as mentors—just about anyone who stands in an instructional relationship to another character, in fact.
1) Teaching is a performance art. The most useful advice I ever received about going up in front of a class is to treat it like acting. It has several advantages. It enables a teacher to act calm and professional, or stern, or enthusiastic, as the class/student calls for, when she might be very far from feeling those things. It lets her conceal personal opinions or problems that would interfere with her teaching. It sharpens her focus, and can partially remove her from the setting, so that, if a student gets upset with the bureaucracy and not with her, she can avoid taking it personally.
In a fantasy setting, where the instruction is most often done one-on-one, the biggest use of this would probably be to remember that what your student sees is not necessarily what he gets. Just because the teacher might be supernaturally calm with him doesn’t make her supernaturally calm with everyone. It doesn’t mean she’s only ever cared about teaching, or about delivering this Special Chosen Orphan to his destiny, and has never had a family, friends, lovers, a spouse or children, or other students. That’s the main place where fantasy characterization of mentors falls down, I think: it makes them far too one-note, replacing them with the role of Teacher instead of a person. If you think of them as actors instead, with one facet showing in the classroom or training ring but other facets visible outside them, then they inevitably become more nuanced.
2) Teaching can be improvisational. Yes, some training plans are detailed years in advance—and a lot of fantasy mentors do seem to be the kind of people who would do that (which doesn’t explain why they always seem to lose track of the Hidden Heirs and only come dashing in at the nick of time to save them from the Dark Lord, instead of properly and calmly collecting them months ahead of schedule). But even then, a difficult, swift, or slow student can necessitate changes to the plan. Other teachers will create their lessons on the fly (hi), or start off with one and alter it when they realize it’s not getting a response from the students. This can help liven up training scenes that are far too mechanical, such as potted lectures given to characters who’ve already been shown to have poor memories and little interest in long conversations, or a series of sword drills that repeat over and over and bore the reader. In an academy or school, granted, one teacher might handle so many students that she’s forced to create a kind of assembly-line process. But many encounters with mentors in fantasy are individual, on a journey to save the world or while preparing in one particular skill, apprentice-to-master. It makes no sense to have the mentor ignore all signs of individuality in her student and just steamroll ahead without ever turning aside, unless she’s meant to be a bad teacher.
Such non-scripted encounters can also bring out more depths of characterization in the mentor. (Characterization of the student is usually not a problem, because most of the time the student is the protagonist). Go off the rails for a little while. If the mentor is supposed to be a good teacher as well as a master of whatever it is the student wants to learn from her, believe me, she’ll notice when someone grows bored of her lessons. She might not always know the best way to fix it, but that will not prevent her from trying.
3) Yoda the sole model for mentors is not. I find the mentor who is always calm, detached from his student, and perfect in his advice an irritating stereotype. (The second most irritating one is in point 4). No, he doesn’t have to be like that. Really. Nor does he have to be the absent-minded professor, or the teacher who cares so much about a less talented counterpart that he neglects the brilliantly talented protagonist. (Tangent: Can we please stop it with the students who are wonderful and brilliant but unfairly denigrated by their jealous teachers and classmates? Strange as it may seem, sometimes there is an actual reason for a poor mark on a paper or a refusal to pay as much attention to someone as they’d like that is not based in jealousy. For example, the other classmate may need more help, or the paper may be brilliantly written but lacking in original thought).
If the teacher and the student have a relationship that lets the student see more than one facet of the mentor, then the mentor should be less than perfect some of the time. He may try to cling to his professionalism, but lose it because he’s being called on to play a parental role as well as a professional one. He may try to bullshit his way through areas outside his expertise and wind up totally screwing them up. He may encourage a student to try something he thinks is beyond her abilities, not because he secretly wants her to fail, but because he thinks the challenge will make her draw on hidden reserves of strength—and then she fails, instead, and the teacher has egg on his face, too. He may split his time and responsibility between his student and someone else, like a child or friend, and not deal well when his student comes to him whining yet again that she can’t get this spell right, and can he pleeeease help her?
The ideal of calm, enlightened serenity may be another reason that so many mentors appear less than human in fantasy fiction. Break it, and an interesting, actual, fallible person can emerge.
4) If he keeps secrets, he better have a damn good reason. Gandalf did. Telling everyone in sight about the Ring would have jeopardized Middle-earth, and some of those who did know the truth in safe circumstances (like Boromir) didn’t understand why they shouldn’t just take it and set up against Sauron.
On the other hand, as soon as he had the truth about the Ring pieced together, Gandalf came and told it to Frodo, because he had to know about the danger. None of this nonsense of holding secrets over his head and saying, when Frodo asked why he had to leave the Shire, “You are not ready to know yet.”
Meanwhile, characters like Jordan’s Moiraine, Goodkind’s Zed, and other “wise mentors” in fantasy run about holding knowledge that could help their students secret, because God forbid the protagonist, and thus the audience, find out about the information when it is actually useful. No, the Dark Lord’s soldiers have to attack first, the protagonist has to show off magic that nearly gets her or someone else killed, and their lives have to be torn to shreds and the people who raised them revealed to be only adoptive parents, before the mentor releases even a scrap of information. And even then, is it something like, “Here is the magic you have and how to control it?” No. Instead we get, “Here is the history of the world going back 6000 years.”
Most of the time, the only reason that the mentor doesn’t tell the protagonist that he’s really her grandson, or that he’s really the savior of the world, or what he has to do to control his powers, is because of the author’s ill-advised attempt to set up a mystery plot. Oooh, we must save the knowledge for later in the book and a Dramatic Revelation!
Bah. That goes against the primary responsibility the mentor usually has (keeping the protagonist alive), because, stumbling blind through the dark, he can’t protect himself or other people as well. And a teacher who hides information from his students and then blames them for failing the test because they lack it is automatically a bad teacher.
In case you can’t tell, I don’t think the standard reason—that the information is dangerous for the protagonist to know—works well at all. Usually, the protagonist is in danger already, and the only way he can get a handle on the confusing and mysterious events happening around him is to know more, and the frustration over being told not to ask questions leads him straight into the heart of more danger because he tries to solve the mystery on his own.
…Come to think of it, that might be another reason that fantasy authors are addicted to this sort of plotline. After all, a hero blundering around blind makes for Dramatic Moments.
Ask yourself whether your mentor is fulfilling the duties of his or her position. It’s always better to keep characterization consistent than to create an Idiot Plot just for the sake of delaying a revelation.
5) Know why the mentor is teaching the student. Sometimes the answer is, “Her parents are paying me rather a lot of money.” But, since that is refreshingly simple and honest, it is, alas, not common in fantasy.
Does he love teaching? Then show that he does. And no, the way to do that is not to have him just agree with and admire the student. He’ll sometimes frustrate her, or trip her up, or challenge her, and that does not make him a bad person, much less a bad teacher. The teacher who just claps his hands and smiles is a cheerleader, not a mentor.
Is he doing this to save the world? Then have him act in a way consistent with that. That, again, allows for a wider range of behavior than mentors are usually permitted to have. He might care more about the world than the physical or mental condition of the savior at the end of the saving, and bam, you have a gray character right out of the starting gate. He might be working to fulfill a prophecy, and in that case he’ll probably pay attention to what the prophecy says, or at least pay more attention to that than the whims of himself and his student. He’ll probably try to protect her, rather than just letting her wander away from the campsite Because That Makes A Good Plot. He may work to discipline her as well as protect her, so she learns not to be stupid. That in and of itself would make an astonishing change of pace for all those books involving rebellious teenagers or sarcastic adults who never recovered from something that happened twenty years ago. Most of the time, the teenager or sarcastic adult is Right, and discipline is inherently Unfair. (A lot of the time, I think a distinctly high-school mentality pervades books like these).
Did he make a promise to someone else? Then he may have unrealistic expectations of his student; maybe he knew her mother, and he expects this girl to act just like her, and is rudely disillusioned when she doesn’t. Maybe he does grow to like his student as a person, but still holds that promise as more important than her desire to chase the mysterious stranger into a high canyon with lots of places to hide in ambush. Maybe he wants to pass on his skills and get out of there as soon as possible, and thus he keeps their relationship as one-note as possible.
Not knowing the mentor’s motive makes the whole thing much trickier—and, most of the time, stupider—than it needs to be.
6) Where and how did the mentor learn her skills? This will make a difference to how she tries to teach her student. She may favor the method she learned by, and impart it exactly. She may dislike it intensely, and go in a diametrically opposed direction. She may think its time has passed, and try to update or modernize some parts of it. Whichever way you choose, it involves thinking about her schooling and her personality as well as about what the protagonist needs to learn.
Also, just a point that thinking about the mentor’s training can prevent: Most of the time, the mentor will be more experienced and knowledgeable than the student, unless she is teaching something she can talk about only in theory, while the protagonist has actual practice (like the protagonist possessing magic she’s studied but can’t wield). I am wearing the Ms. Obvious cap again, but another thing I’m sick of in mentor stories is the student jumping miraculously past his or her teachers, and forcing them to respect his or her Mad Talents. I promise, the story will not be ruined if your hero is not perfect at everything the first time around. In fact, he can actually take more than a few days to learn, and that’s okay, too. Yes, really. Really.
If nothing else, think about this: Why do you need teacher characters if your protagonist is just going to surpass them the first time out? And too often, I think the answer is: so that there can be people standing around slack-jawed when the protagonist does something wonderful. I could write a long entry under: Moments When the Protagonist Awes Other Characters, Curing the Addiction To.
No idea what will be next, yet.