(slightly expanded from my twitter thread this morning. As usual this is not gospel truth, but things that happen to work for me. Do feel free to take what you want from this and throw what doesn’t fit)
This morning’s thoughts: likeable characters. I think they’re overrated.
We can argue and should argue a bit about what makes a character “likeable”. It’s highly subjective, partly dependent on moral values of society, partly dependent on people: I happen not to care much for arrogant characters, so any character that has this flaw has got an uphill climb to be sympathetic to me. On a societal level, because misogyny is still embedded in the way things work, men in positions of power doing terrible things in service of a good goal are generally seen as ruthless, women as bitches.
However, for me the root issue with “likeable” is that I don’t think characters have to be likeable. For me, they have to be interesting, which isn’t quite the same. This actually ties into a larger thing: the end goal of writing is to hold the reader’s attention. And the thing is, there are many, many ways to do that: which one you use depends on you as a writer, and the audience you target, and the conventions of the genre you’re writing in, etc. (a lot of writing advice is about tools and tips and things you can use to hold attention–they’re not so much unbreakable rules as ideas to keep readers turning pages).
If we’re just talking characters: you can make readers care about what happens to them, which is the “likeable” part of the equation. But you don’t have to. You can also make readers wonder and fear what they’ll do next. You can, conversely, just decide you don’t much care about characters and that the important thing is unfolding the setting around minimal portraits. You can also decide that the twists of the plot take precedence over the characters. Again, valid choice. (you need a minimum obviously. No characters at all usually makes it hard to engage the reader because we’re wired to pay attention to that. We’re also wired to find people or people-equivalent in stories so it tends to happen regarless of whether you plan for it or not)
A few tricks I used for terrible characters (*cough* Asmodeus *cough*): it helps if they’ve got a code, even if it’s a horrible code, because we tend to value highly people who stick by principles. It also helps if their goals are things we approve of, even if the means they then deploy to achieve them are horrendous, again because–as a society–we tend to judge strongly on intent: Magneto wants to protect all mutants from being persecuted, Holland in VE Schwab’s A Darker Shade of Magic series wants his London (which was unfairly shut off and devasted) to be prosperous again. Asmodeus in my own The House of Binding Thorns wants to protect his own House and his own people in an environment of scarcity.
Sarcasm and honesty also help: again, values vary, but hypocrisy in our societies is particularly hard to swallow. Sarcasm/irony in particular have high correlation to fascination: we pay attention because we want to know what the characters will come up with next, and because it feels like they’re speaking truth and/or seeing things more clearly than the other characters (they may not actually be seeing things more clearly, but that’s another issue!). Think of Spike in Buffy the Vampire Slayer: part of his appeal is that he always seems to puncture holes in the main characters’ earnest plans.
Power dynamics–how terrible characters behave with their inferiors–is an easy but neat trick. The expected is they’ll be terrible, so if you buck it you get a lot of extra mileage (plus, I never really believed the dark lords who kept killing their subordinates would have many subordinates left after a few months–everyone would just leave and find a more reliable employer!) 
Another easy one is the reedemable feature, though “redeemable” is again highly dependent on people (one person’s redeemable feature is another’s breaking point): easiest one is their caring about people, especially forgiving them if they do something terrible character doesn’t approve of (you’d be surprised how often, in media, terrible characters turn out to only pretend to care about their loved ones, or to kill their loved ones as soon as they do so much as stray from the path).
Note that the goal of all of this isn’t to actually redeem the character: all of this is way below the hard work, atonement and change of heart required for redemption. The goal is just to make sure the reader gets invested into the character–you lose, as a writer, if they wander off or throw the book across the room because the character is so horribly a turn-off and the plot so uninteresting they’d rather be doing something else. And yes, a lot of this–like “likeable”– is still highly subjective: again, the trick is appealing to your readership (trying to appeal to everyone with “universal” values has, at least for me, always resulted in character design by committee: the results are bland, unlikely to make anyone throw books at all, but also unlikely to make people want to fight for your characters!).
Another word of warning that you probably don’t want to try this trick with every single character in your novel/short story/etc.: terrible characters tend to shine best when they’re mixed with other characters that readers care about. Or at least characters who are decent. You can make every single character in the novel terrible–it’s been done and it’s been done with great success–but it’s going to be a more difficult tightrope to walk because terrible characters will have no one to be contrasted against, and no one they can bounce off, either. A little goes a long way.
So basically, my recipe: give the reader something to cling to, make sure that said thing doesn’t break halfway through the plot (and if it does, replace it with something else before it completely breaks)–and throw in enough unexpected to be surprising. That, and doing the usual prayer of the writer aka “please please let everything not implode in mid-flight”!
(and yes, speaking of mid-flight: I have a book that just came out. It’s set in a ruined and dark, decadent Paris; it has dragons, Fallen angels, alchemists, revolutions and betrayals; a terrible character and decent ones, and I had a lot of
anxiety fun writing it–I would love it if you checked it out. Sorry, had to say it. Sales are how I get the chance to write other books °=°)
In The House of Binding Thorns I balanced the power dynamics of a particular scene on a knife’s edge: I had one scene which involved one character in the power of a terrible one, and I deliberately played with the expectation of terrible things happening to create tension–in particular, at one point, consent is asked for, which very much went against the grain of such scenes. It was a deliberate choice.