I love smart MC in general, even if they're not the strongest.
Though I'm not sure if I can write them since I'm lazy and don't like to use my brain much.
What do you think is the easiest, most low-effort way to write an intelligent main character well?
How to write an intelligent main character when you're lazy and don't like to use your brain? Ai-chan would separate this request into two parts:
1. Character Development
2. Plot Development
For character development, you DON'T create a smart protagonist. Why not? Because most often than not, intelligence can't be seen, unless he wears a lab coat and works in top secret government lab trying to research on how to build an FTL drive. By NOT aiming to make your intelligent protagonist a 'smart protagonist', you avoid most of the pitfalls of Mary Sue-ness that people commonly make when they try to make an 'intelligent character'.
Now that that's out of the way, pick a branch. Yes, that branch looks perfectly fine. Oh you don't like that branch? You want the one next to it? No? You want the one your sister's holding? Fine, take it, you bully!
This branch here is basically your character's knowledge tree. Pick one, just one, do not pick two, do not pick three. Just one. Your character is a mechanic? That's good, the branch you've picked is mechanic, therefore, you can make your character a genius in mechanical engineering. He should know how to fix an engine or tune up a car to go faster. He can probably even be a racing champion, as after all, he must've driven his own hypertuned car and being a champion is simply a personal accomplishment, not an entire skill tree. You can even make him able to understand and fix alien starcraft engines because he's the genius mechanical engineer, it's well within his scope of interest.
What if you choose the scammer branch? That can work too. It's probably more versatile than the mechanic branch, but it is unlikely to be as specialized. So while you can bullshit in a way that he can fix a car, probably because he learned that in order to scam people, he couldn't possible build a car from scratch on his own. His knowledge and skills wouldn't be so extensive that he can do that.
And knowledge and skill are important. In relation to how long the character has worked on those skills, there is a finite amount of work that they could've done to achieve that level of specialization. A soldier who has been soldiering for 20 years would most definitely be better at soldiering than a mechanic-turned-soldier who spent the past 20 years being a mechanic.
As for plot development, the first thing you want to do is make sure that it rarely goes the protagonist's way. By this, you try to actively remove everything that helps the protagonist. Because when everything goes the protagonist's way, you're not making an engaging story, you're making a Mary Sue. If you want to do it, do it, it's your story. But don't expect readers to like it because Mary Sue characters get boring after the first few times.
If you do not know how to do this, make a 6-sided die. Write on a notepad somewhere something along the lines of:
1. Help arrive
2. More enemies
3. Deus ex machina
4. Enemies stumble
5. Mortally injured
6. Betrayal
Now let's say that your character is a cook, which means he has access to the entire cook/chef branch. You threw the dice, and got a 6. Well, shit, man. Not only do you have to fight a powerful monster, you're also betrayed by your own companion. Shit what should you do? This is when you use the cook/chef branch to show that the protagonist is intelligent.
So let's look at the cook/chef branch:
1. Cooking
2. Cutting
3. Marinating
4. Preserving
5. Socializing
6. Haggling
7. Fast hands
1. Let's talk about cooking, while it's illogical to cook right now, every travelling chef will carry his own cooking ingredients, if he assumes that the place he's going to won't likely have the ingredients he wants to use. However, some of the ingredients that we use to cook food for humans are really avoided by other creatures. For example, garlic. Most carnivorous animals with good nose absolutely hates garlic and it can even be lethal to canines. But if they hate garlic, why would the wolves chase your character in the first place, you ask? Probably because your character carries garlic in a ceramic bottle with a stopper, so there would be no smell coming out and they wouldn't know that he was carrying garlic.
2. How about cutting? Well, the simple consideration is that your character is good at cutting things and can fight the monster, right? That's not all there is to it. If you're a cook who has been cutting meat for a long time, you would instinctively know about meat parts because you pretty much study animal anatomy every single day while you're at work. While not every animal has the same parts, every animal follows the same rules. There are ligaments, veins, muscles and bones. Someone who cut up animals everyday would know that the belly is always the softest because it doesn't do any work. They would know that the armpit (or legpit) are always unarmored and will almost always have large blood vessels running through there. So cutting the legpits will almost always cause the creature to bleed to death.
3. Marinating is useless in this case. However, just like cooking, you'd probably carry ingredients for marinating. Onions are common for marinating and dogs hate them. Don't marinate the meat you're feeding your dogs in onions. You could cause their blood vessels to rupture! Then again, if you already have meat marinated in onions and garlic, you could feed the enemy dog with it and watch as they pass out and die.
4. About preserving... Ai-chan doesn't know. Maybe you can just lure carnivorous monsters with preserved meat?
5. Socializing is important to chefs who regularly converse with patrons. Maybe your protagonist can talk his way out of danger.
6. Haggling is similar to socializing, except you've learned the fine art of scamming the other side down to their drawers.
7. Most chefs who work in busy kitchens would have fast hands because otherwise they'd spend a very long time getting the food out. Fast hands are very useful when you're fighting.
You're asking why we haven't addressed the betrayal yet? Let's address it now. Read the above sentences and apply it to the traitor instead of whatever carnivorous monster your character is facing. The end.