I will try to keep the guide as short as possible, But first things first, let's talk about Darius.

Darius is an AD bruiser, which makes him able to deal and take damage, but he is a slow champ with no speed boosts, however his E Apprehend is a gap closer that can pull multiple enemies to you, slow them and give you Armor penetration , which can help you against champions like Yasuo, Vayne, Shen, you get me, champions that have a dash.

Try to avoid the champions listed below.
Master Yi, Vayne, Kalista, Teemo, Kennen, Trundle.

So about Darius' abilities, his passive Hemorrhage is a super strong passive, and Darius' main damage output, it's a damage over time bleed effect, that stacks up to 5 times, and at 5 stacks of Hemorrhage, you gain Noxian Might.

When you have Noxian Might, your abilities/basic attacks give 5 stacks of hemorrhage on the enemy instantly, and grants you bonus AD.

his Q Decimate deals damage and heals you if you hit with the blade of the axe.

If you hit with the handle of the axe, you will deal 100% damage, the blade deals 200% and heals, so always try to hit with the outer part of the Decimate.

Moving on to the W Crippling Strike is an enpowered basic attack.

It deals more damage based on it's level and your AD, and slows the enemy, and more importantly is an autoattack reset, which means you should always autoattack before using your Crippling Strike.

His E Apprehend is Darius' only gap closer, it can pull multiple enemies to you, slow them and give you armor penetration, depending on it's level. This is almost always used to pull targets that are running away from you, so you can DUNK them.

Now the legendary ability, Noxian Guillotine aka DUNK is the holy ability of Darius.

FIRST OFF, remember, it deals TRUE DAMAGE, which means it does not matter if your enemy is a tank, it will always deal the same amount of damage.

Secondly, always try to kill your enemy with Noxian Guillotine, since it's cooldown resets and you gain Noxian Might.

Now into the actual ability.

Darius' R Noxian Guillotine is a lock on ability, dealing true damage scaling on your AD, and how many stacks of Hemorrhage on the enemy.

NOTE: When you dunk someone, you have to hit the next enemy for the max damage on your Noxian Guillotine to deal max damage, because you need the stacks on the enemy.

For runes, i like to take 9x AD Marks, 3x AD Quints, 9x Armor Seals and 9x Magic Resist Glyphs, nothing much to really say here, pretty simple stuff. AD marks and quints for early damage, Armor seals and Magic Resist glyphs for early tankiness.

I'd still go with Stormraider's Surge because of the huge movement speed buff, but you can also use Grasp of the Undying, which i don't really recommend vs anything that can kite you, and the new keystone of S7, Courage of the Colossus . But if you pick Courage of the Colossus , remember to use your Apprehend, since it's your only hard CC.

PROS:

+AD Bruiser: Deals damage and can take damage.
+Extremely hard to lane against, insane 1v1 potential.
+Can easily 2v1 when ganked.
+Hard snowball.
+Strong in general.
+Easy to play.

CONS:

-Low mobility, easily kited and chased. (Why i take Stormraider's Surge )
-Easily predictable.
-Jungler camps you just because you're darius.