On lane you can always dominate no matter what matchup you have. Because of your passive early trades are highly recommended. If you are up against a melee champion stand between him and your minions and kill him if he tries to last-hit.

Agains ranged champions you can try to trade as long as you are on low level and then wait for ganks. Always try to initiate a trade with your E as it is your only gap-closer.

Against melee champions u can initiate a fight with any basic ability. You can just walk up to them autoattack them a couple of times and combo once to get max stacks on them.

For your Summoner Spells you can take Flash with either TP or Ignite. Although I prefer TP since you will have more map presence, you can take Ignite if you want to play even more aggresively on the lane and go for a pretty much secured first blood.

Q:Decimate
Darius' Q is probably one of his most important abilities since he gets a heal off it and deals tons of damage. Try to ALWAYS hit the enemy with the blade even if you dont need the heal. This ability is also good if you are getting ganked; just Q both of your targets and get the heal and maybe you can continue the trade and try to get max stacks onto one enemy followed by your R which means a pretty safe double.

W:Crippling Strike
There is really not much to say about his W since its just kind of an empowered AA. Anyway you should try to use it as an AA reset to get Max amount of stacks o the target in minimal time. Its best implemented in the combo the following way: E, AA, W, AA, Q, AA.
That way you will get 5 stacks of Hemmorrhage on your target in about 3-4 seconds, activating your passive and giving you extra AD for 5 seconds.

E:Apprehend
The only thing about the E is that you should really hold on to it since it is your only gap-closer and also the only CC. Try to avoid fighting ranged champions with kiting potential if you dont have your E since you are probably going to die. Also try to interrupt channels and similar with your E. For example a Jhin ultimate or Xerath ultimate. Also if your enemy laner tries to go for a bot gank with tp you can interrupt it and kill him.

R:Noxian Guillotine
When it comes to 1v5 Pentakills Darius is probably one of the first guys you think of. That is because his R gets a reset whenever he kills a target with it. In a teamfight you should wait for your team to engage since you cant really do anything there. For example if you have a Kalista and Alistar on the botlane wait for their R engage. Afterwards you can just pull everyone to you and try to get a kill with your R as soon as possible. As soon as you get a kill your passive kicks in allowing you to apply max Hemmorrhage to all enemies hit by any abilities or AA. After that its pretty much a won Teamfight since you just have to make sure your R executes the enemy (what shouldnt be too hard since its going to deal about 800-1000 true damage).

I like to start off with a Black Cleaver since the Armor-pen is really good on Darius. Although you can vary your first item based on matchup its definitely a good start. The second item is either Steraks Gage or Dead Man's Plate depending on how your lane goes. If you are behind go for the Dead Man's. if you are doing good go for Steraks.
After you have these three items you can adapt to the game. Go for Spirit Visage and Banshees Veil if the enemy has mostly AP champions. Randuins and maybe Warmogs Armor if they have mostly AD champions. And if they have both, which is going to be the case in most matches, buy both armor and magic resistance.

For Masteries I take 12/0/18 and choose Grasp of the Undying as Keystone.

Ferocity:
Sorcery for more damage especially on your Q, Double edged Sword since taking a bit more damage is definitely not a problem, Vampirism for lifesteal and more sustain and Opressor since both your W and E have a one second slow of 90% / 40% on them.

Resolve:
Recovery for more lane sustain, Tough skin adds up to your tankyness, Runic Armor makes your Q heal even stronger, Insight since TP has a relatively long Cooldown, Legendary Guardian since you are going to experience a lot of 2v1 and 3v1 scenarios as Darius and Grasp of the Undying for EVEN MORE lane sustain and because its a really good keystone.

In the seals I have 9 Armor seals. In the glyphs I have 9 Magic Resist glyphs. In the marks I have 8 AD marks and one crit mark because if you are lucky enough to crit using your W the trade is pretty much won. And last but not least for quintessences I have flat AD.
You dont have to make another extra rune page for Darius since you can just use the ADC page and put in AD quints instead of attack speed quints.

If you dont have the Dunkmaster Darius skin you are not allowed to play Darius cause lets be real, what is more awesome then dunking your enemy?