Here at TV Tropes, An Aesop is what we call the moral of a story. A lot of people, both on and off the Wiki, complain about stories with morals, but there are plenty of ways to write an Aesop well. You just need to be aware of a few things.
Don't make the Aesop too contrived.
There are several ways that the moral of a story can be contrived, and all of them are generally a problem. Some of them make it seem like the story is rubbing the Aesop in our faces, and other times it just seems like bad writing. Here are a few ways that an Aesop can end up seeming contrived:
- It's out of place for the series: In a standalone story, this wouldn't be a problem, but keep this in mind if you're writing a TV show or a series of books or anything else that could be described as a "series". There's a reason why episodes of sitcoms meant to deal with serious issues have been criticized for being too dark and humorless. If your series is mainly sci-fi or fantasy, you might want to consider keeping the Aesop confined to a subplot, because if the "threat of the week" is usually aliens or dark magic or whatever, and in one episode/book/whatever, it's drugs, people will tend to dislike that story line.
- It relies on the ones learning the Aesop being out-of-character: If you're going to teach an anti-bullying Aesop, don't have the nicest kid in class suddenly turn into The Bully. If you want a story with a lesson about not giving up, don't make someone need to learn it who normally never gives up. And don't have two or more characters argue over something they normally would be chill with, or have an argument lead to them stopping being friends when they've argued about worse things and remained friends.
- The characters not learning the Aesop are out-of-character: You might think it is funny to enforce the trope Even Evil Has Standards and have the villain be repulsed by what you want the audience not to do, but often this ends up seeming too contrived: after all, if a villain literally kicks dogs, would you expect them to be that worried about hitting humans?
- You, the writer, didn't do the research: If someone out there knows a fact that you got wrong, they might decide your Aesop is meaningless- after all, why listen to an author who doesn't know what they're talking about? Examples of common research failures are a Disease-Prevention Aesop where viruses live on surfaces or the weather makes people sick, a Drugs Are Bad message where people trip on mild drugs like pot, or a Too Smart for Strangers lesson which acts as though strangers are the only people who could molest or kidnap children.
Avoid demonizing the people who do the thing you want the audience not to do, or the thing itself.
Some things are legitimately bad, but demonizing is making a person seem very bad for doing something pretty minor, or making something seem worse than it actually is. For example, a religious message might portray atheists, people of different religions, or sometimes even agnostics, as being bad news or anti-[insert religion here], while in reality, many religious people are tolerant of other religions, many atheists are tolerant of religious people, and the very definition of agnosticism is basically not caring either way.
If the moral isn't "don't do X" so much as "don't do X too much" or "don't do X in a bad way", then say so. Yes, it's bad to eat too many sweets, but eating sweets in general isn't bad, yes, it's bad to camp in a way that's bad for the environment, but you don't want to make the story seem like it's trying to say that camping in general is bad, and not all video game nerds are slobs with health problems who think Nature Is Boring.
And be very careful about problems which often have a psychological cause, such as drug addiction.
Communicate the Aesop properly.
While you don't need to outright have a character say, "The lesson to be learned here is...", you actually need to communicate what's going on. If you're writing to kids, you have to make sure they know exactly what a drug is, that germs are not tiny, intelligent, evil creatures who fight an army of immune system people in your body, and that a "bad touch" isn't just any unwanted hug or whatever. If you don't communicate, you'll likely end up with everybody being very confused and possibly not even knowing what the moral is meant to be.
Don't make the story just an excuse to deliver the Aesop.
Stories like this tend to be seen as boring and overly preachy, and if it's one story in a series, it runs the risk of fitting the "doesn't gel with the tone of the series" problem mentioned above. Quite often, the only people who like a message that's nothing but the moral are people who agree with the moral or people watching/reading the story to laugh at it, which means that you're either preaching to the choir or making people laugh at what you wanted them to take seriously. A good way of testing to see if your story is "all moral, no story" is asking yourself what the story would be like if the moral was removed.
Be wary about having highly unlikely or impossible consequences for following or not following the Aesop.
The trope for this is Space Whale Aesop, and while Tropes Are Tools and the Space Whale Aesop can be entertaining and/or funny, you do need to be careful.
The reason for this is because most people, if not everybody, will know that the unusual consequence probably or definitely (depending on what it is) won't happen. For example, they might think, "Littering is fine because I'm highly unlikely to get abducted by aliens" or "Fairies won't reward me for not littering because they don't exist." And a Space Whale Aesop of the one-thing-leads-to-another variety is likely to be seen as a Slippery Slope Fallacy.
The best way to avoid these pitfalls is to make it clear that you're not just saying, "Do or don't do X because this impossible/improbable thing will happen". For example, you might show fairies as only one of the creatures affected negatively by littering.