This is my first guide, but it is made with the confidence of a bronze master Darius player.

As a reminder, this is only for good Darius players.
;)

9x Attack Damage - This will keep your damage within acceptable levels early game when you start ruby crystal.
If you start doran's shield, I might laugh at you. Darius doesn't hide behind shields.

9x Armor - Early game strength when your opponents will believe they can out-damage you. Scaling or Health won't quite give the same effect unless you really want to play that long con.

9x Scaling MR - The mages might think they can take you where their AD top fails. This will remind them who you are. (Dunkman)

1x AD Quint, 2x MS Quints - Run fast, dunk fast.

Fervor of Battle might be taking hits each patch, but it is still a healthy Keystone, as compared to the more predictable three/four-hit passive Keystones. It's constantly active, and doesn't go on cool-down, making it reliable, and a good incentive to practice keeping your bleed stacks up.
Everything else is just typical for ad-tanking, the new increased defense and offense on engagements are pretty nice.

Titanic Hydra - This weapon gives you a very good auto attack refresh, adding on 200-500 damage as you progress throughout the game. This is good for towers, where you can aa-w-Titanic-aa for a good 30% of tower health before anybody can get back to it. Likewise, it's a fair deterrent to anybody hiding in the back row, and can offer a large swathe of death if you can pull 3+ enemies, setting you up for an easy w-q-r while they try to wrap their head around having just been slapped by 500 damage each without having taken anything but an auto yet.

Boots of Swiftness - Honestly you can take either these, tabi, or mercury's, but these are typically the most rewarding, allowing you to keep on your enemies, or get away quickly if necessary. Tabi are good for people like Jax, Jinx, or Tryndamere, Quinn, etc. No shame in buying it if you need to, you won't get any other defense until well past your Cleaver.

Black Cleaver - Take this second, as maxing your e second should take care of any armor building for the meantime. This is another bonus to your perpetual quest for stacks. That makes something around 67% armor pen with masteries, enough to make Vi jealous. And your enemy laner will thank you for not making their death too slow and painful.

Randuin's Omen - Your only real threat is an enemy who can keep their distance, so this will definitely mitigate that. The attack speed slow is one thing, but the aoe slow is another good bonus to keep them within range.

Spirit Visage - New q is pretty good, yeah? This makes it 20% better, and gives the added bonus of making red buff greater, and mages lesser.

Warmog's - Spirit Visage makes this greater too, and your Titanic Hydra will thank you for the extra 100 attack damage you just gave it. This is why you do not build many further attack damage items, as every hp item will bolster your Titanic Hydra's attack power to compensate - that and you get an extra 10/20 ad for Noxian Might each level. So keep your stacks up. STACKS.

Decimate goes up to 1.4 AD scaling once you level it to max, so it's definitely a good start.

Crippling Strike got a good bit of a nerf with the rework so it's not as much of a priority to level up. Leave it unlevelled, as it doesn't scale up with AD anymore either.

Apprehend levelled second will keep your AD up as they build armor, and the cd reduction is very nice for quick engagements.

Teleport for greeting their ADC, and flash for fun flash-q combos. Don't miss.

Play this build.

DUNK.

Execute the entire first warrior wave with a q, leaves you some good room for some early trades.

Once you get tiamat, it's a trivialty to lane.

Ask your enemy jungler if you can have his red.

Pros -

• Able to build tank without sacrificing AD at all.
  
• A healthy two slows and self-heal based on missing hp can keep you in the game for much longer than an enemy might think.
  
• Ultimate has slightly more range than it lets on, and puts you in a static range for a good follow up if you're a little too far away to apprehend.
  
• Ultimate also lets you shoot for three if they try to flash or dash away too slow.
  
• Noxian Might gives you a ton of AD consistently throughout the game, enough that you won't even need your ult half of the time.
  
• People will think you're really good even if you really aren't.

Cons -

• If you play predictably, you'll get played predictably.
  
• Poking and bully champions will give you trouble if you let them.
  
• Not too many escape options. Go big or go home.
  
• People will expect you to keep being really good, even if you aren't.
  
• If enemy likes to be close too, you'd better be able to keep them in your hand.
  
• Darius is banned often because he's a big scary man with an axe.

-Kled, the Wisest of All Yordles

Now, you aren't here to take all of the glory, but the rest of your team are indeed just coattail passengers.

Give your ADC a kill or two, murder your top laner, and take mid tower. When in team fights, prioritize getting 5 stacks as quickly as possible so your immediately following q dishes out a good 500 damage bleed, and pray to god that your allies don't try to get an easy kill in the midst of a large fight when you're lining up to dunk, or else all of those stacks will go down the drain and you'll have to let them die while you walk home. Bear in mind that once you hit five stacks, you are the main threat, so be prepared to take all the aggro.

Let them set you up with stuns and slows, but don't go and waste your e until they've burned flash. Always try to open with aa-w if you can help it.

I hope this build helped you somewhat in learning how to Darius proficiently.
I got tired of seeing all of these builds promoting Sterak's, base ad boost is good, but damn it's embarrassing.
Like starting black cleaver.