ALL AD RUNES AND QUINTESENCES

21 9 0
focus on damage of course.

Boots and 3 health pots
Go besserkers greaves to take down turrets quicker and better 1 on 1 action; Darius is about dealing out the hemorage faster so you can dunk them before they can get a combo off of you.
Get a ruby crystal or giant's belt depending on what you can afford. If you can, build phage first. If you are soloing, you might want to strap on a giant's belt to sustain your lane longer and get more farm and not fall behind on levels.
Turn your phage/giant's belt into a frozen mallet. Now, while this does give you some damage, 30 damage is not a lot. It does compensate with its 700 health, but don't let that be your only damage item.
Next build a brutalizer and turn it into a black cleaver. This helps you with damage, armor pen, and health.
From now on, keep true with the damage. If needed, get some armor like an Atma's impailer or get some magic resist like the maw of maltorius. Either way, don't get something that only gives you health. Darius looks like a tank but he's not. If you build Darius only tank then you are wasting his true potential.
After the black cleaver, get a blood thirster for more damage. If you are still laneing at this point (which is rare) then this will help stay in lane longer. If you find yourself hugging tower with low health or even below half, go jungle and get your BT stacks up and get yourself some health. Also, farm on minions for stacks and lifesteal
Next, get a BF sword or a pickaxe and build infinity edge. Don't get a cloak of agility because Darius won't benefit from it as much as an ADC.
At this point it should be clear who on their team is fed or not. If it's an AD champ pick up an Atma's impailer. If it's an AP champ, pick up a Maw of Maltorius.
As for your sixth item, go crazy. Get some attack damage preferably such as a second blood thirster. However, if they have a 30/0 AP yi, go ahead and get a pure magic resist item. Or, if they have a 30/0 Xin Zhao who is eating turrets, get yourself a Thornmail.

Q,E,W, then max out your Q, then your W, then your E, upgrading your ultimate as often as possible of course.

If you are soloing, take Teleport and flash, If you are laneing with someone, take flash and ignite.

Draius is not an attack speed carry, but a bruiser carry. A fed Darius is a good Darius. KS is your friend. If your team is complaining about you kill stealing, remember that if you are fed, you are helping your team win. Now, late game don't try to ks as much. Also, remember your passive. 5 attacks or abilities=double damage on your ultimate. this includes your decimate and your cripple. This is also why you want beserker's greaves, so you can deal out more hemorage quicker and take em down with your ultimate before they kill you.

Remember to farm while laneing. When soloing, just stay back and farm and level up patiently until you get to level 6. Meanwhile, poke the enemy champion(s) with your decimate. Your decimate does 50% more damage when they hit your blade as opposed to your handle. When you get to six, either ask for a gank or pull em in your self, cripple them, decimate them, and ult them.

As said before, ks early game and share late game. Your pull also makes for a good teamwork tool.

Get red buff often and blue occasional. If you find yourself running out of mana, get blue for more sustain and more dunks.

One of Darius's main cons is his lack of ability to escape situations as easily as someone like Lee Sin or Jax. One pro of Darius is that you can kill them all before they kill you. When in doubt dunk, and you could survive.

If you know you are about to die, dunk. Do as much damage as you can before you die for someone else to come clean up and give you an assist, or ignite them and maybe pick up an after death kill from your ignite and your bleed. They might get a kill, but they will be giving a kill and an assist. Even if you are putting your ultimate on cool down, by the time you come alive and return to lane, it will refresh.