I have run a couple of campaigns with a few of my friends, and these people are genuinely interested in Dungeons & Dragons.

However, no matter what I do, they will not focus on the story, instead treating it like some sort of slaughter-fest. They do not really kill everything that moves, which is good, but they miss nearly everything in the game because they just fail to interact with it. The only way we have completed campaigns is through me pretty much telling them OOC what to do and where, because they are that lost.

Now, I have read this question ("How can I deal with players who don't consider the narrative?") but it does not seem to answer my problem, as I am posing no challenge nor puzzle. They just fail to pick it up. I am the GM and I have tried to help them in every way I can imagine, but it just does not seem to work. I do not think it is me being a bad GM, because I have played with other groups and that went just fine. Short of telling them "There is a quest here, you should go here and talk to Joe there" what could I do?

For some possibly helpful information, or to just save time, I have tried having NPCs talk to them and hint at so-and-so having a job for them, I have tried having them find letters with a name on it and a note with the start of a quest on it, and they just shrugged and left. I cannot make it any more obvious, and it is starting to affect gameplay, as we are playing one of the official campaigns, with just a little bit of homebrew added (just a bunch of other quests that add some extra leveling up opportunities and loot opportunities).

It's not that we haven't talked about what kind of game we're playing We have actually held several "session 0's" and we do talk about story. We hold an end session around 10 minutes to the end of our game time, and we talk about each other's expectations. One PC is borderline murder-hobo, and he does express his interest to pretty much kill the biggest, baddest thing around. The character is also extremely touchy in game, and will blow up at the slightest insult. However, thankfully, that is only the PC, not the player, and we do all realise that it is just a game. One of the other players just seems... not really willing to contribute to the betterment of the group. We are a band of 4 people.

Short of railroading them, what can I do to get them to focus on the story and pick up on story hooks?

Answers should demonstrate experience or citations per What are the citation expectations of answers on RPG Stack Exchange? and not just be unsubstantiated opinion. What have you done or seen done to address this issue?

A friend of mine actually has quest logs.

So as soon as the party finds a quest (= pointer to the plot), or they make one up on the fly, they write the quest on an index card* and hand it to the players, just like you might have a quest log in a computer RPG. Find the location of the Eyrie, Recover the diamonds from the mountain lair, and so on.

I seem to recall also doing this myself in 4e back in the day, but I can't remember if that was something the system recommended or something I improvised. I think the former.

If the party have a stack of cards with quests written on, they can refer to them and choose which one to follow.

They might not want to follow the quests, preferring to plough their own furrow. But as long as you and they are having fun with that, that's fine too.

*technically they use http://almanac.wiki instead of actual index cards, but the method's the same

You're not being as obvious as you think you are

Something that is obvious from your side of the GM screen is not necessarily so from the other side for all sorts of reasons. I refer you to selective attention for an example.

The three clue rule

You have to give your players at least 3 clues if you want them to follow a lead because they will overlook one, misinterpret the second and maybe work things out on the third.

Forget the story

Just set up a bunch of loosely connected adventures and let the players kill stuff. You can then say "The adventure is here."

Railroad them

Railroads are only a problem when they are a problem - if your players are happy being led around by the nose lead them around by the nose.

Find different players

Some players do not care about the story and never will. If that bothers you find players who do care.

Throw fewer monsters and more non-combat challenges at them.

Sure, with enough ingenuity, players might try to brute force their way through, for instance, the castle gates by killing the guards, but if they were to do so, they'd probably get a hefty bounty on their heads and the king wouldn't dare talk to them. Anyway, I digress.

D&D has a lot of mechanics for out-of-combat interaction, which is where the story is. If you end up spending the overwhelming majority of your time killing things (especially since an encounter usually takes at least 20 minutes), it's no wonder your players will lose track of the story.

Intertwine combat with the surrounding world. I think we often, as DMs, compartmentalize combat and story, but if you take the approach that the bandits have lives outside of thievery and make real and lasting consequences for what happens in combat (e.g. bounties, people avenging their wanton murder, callbacks to previous battles, etc...), players might put some more thought into the world and its story. Combat is an interaction and has just as much potential for story as anything else.

It's also possible that you have the type of players who just like combat and killing things. You might be better off finding players who are more interested in story and less interested in combat.

Move incentives around and add mechanics around the thing you want players to interact with.

By default, 5e has piles of combat mechanics. If a player wants to swing a sword at something, by golly, 5e will tell you what happens.

It has next to no quest/adventure mechanics. And basically zero of it is player facing; the DM can hand out quest XP at some point, but a player is reduced to finding story hints and hoping the DM hands out said XP.

This gives a really long reward cycle that can fail to encourage players to focus on it. Meanwhile, combat has a multiple reinforcing reward cycles -- the player is narrating story right away, each round gives a bit of spotlight and a set of things to do, the combat is done after a few minutes and you get XP and have defeated the foes, etc.

There are many sets of house rules out there that can bring "find and do quests" into the mechanical hands of the players.

Here is one (not mine).

Here is a thread talking about it, more specifically talking about bringing story-based game fail-forward mechanics to 5e, with a lot of "get the players mechanical hooks on story" discussion within, including actual play experience results.

The basic bit of the idea is that you replace the default 5e XP system with one that is based mainly around resolving quests and resolving BIFTs (the inspirtation mechanic in 5e).

During a session you can earn XP by spending inspiration or failing a roll that matters (like, missing every attack in an important fight, or a skill check that has serious impact on the story).

Each session, a player can earn an XP by resolving and changing a BIFT based off the story.

Each session, the party can earn a single XP by gaining a treasure, defeating a difficult foe (EL minus Party Level XP), making a powerful enemy who remains at large, discovering a significant fact, forming a significant alliance. Each of these can only be earned once per session.

Finally, each player can create a quest or mission at any time. At the end of each session, each player adds a point to a quest or mission they have. When you resolve the quest or mission, you gain that much XP at the end of session. So if you resolve a quest/mission in the same session you create it, 0 XP.

What is going on here is that we are structuring the XP system to reward a certain kind of play. Second, we are giving players agency to craft their own quests/missions, and giving them physical tokens to remind them of that quest/mission.

Instead of rewarding them at the end of a quest that you provided, you have players in effect rewarding themselves for finding a quest/mission almost immediately (with the card), then over time (investing points into it), and finally when resolving it.