For the Masteries set as mentioned you can opt for a few good pages, conqueror is the best all around imo as the damage output with it is insane!
you can go also phase rush if you have a hard time staying close to your opponent or grasp for the hp bonus and extra tankiness/damage you get(i usually dont use this as i think conqueror is way better)

Item builds are mostly explained up top.
Never build the same, be adaptive based on your circumstances and be smart!

I mostly run Ghost, as Darius has no problem damage-wise to need Ignite, but you may need Ignite if you go against Heal heavy champions as Mundo or Vlad
Go Teleport if you want the pressure or for a safer laning phase
Oh and obviuously do NOT go without flash

°Pros
-High damage output even if build full tank
-True damage from ultimate
-Ulti resets on kills, giving opportunity for some sweet penta dunks
-Can 1v5 if ahead

°Cons
-Suffers alot from cc
-Gets focused alot
-Kited easily
-Needs to stack passive to be relly impactful

In lane keep in mind that you already won, your opponent just does not know yet, bully hard but try not to overextend as junglers like to camp a Darius so be aware.
if you do get ganked make a quick decision, fight or run, if you play it right you can get some sweet doubles and get that snowball rolling!
If you are playing against a ranged(Teemo, Quinn) play like a ***** until they make some mistake

As a darius your main objective is to get you passive stacked up, you can do this by attacking the same target(focus a tank for an easy stack) or you can ks with a dunk on some low hp target for an instant 5 stack! meanwhile you want to keep using q as you get some massive heals off of it