Early game is very important for Darius,I take ignite top and get first blood before lv3 but that's more advanced stuff,I would suggest you to play it safe until lv6,yes poke your enemy with Q but don't engage recklessly, also make sure you watch out for ganks since Darius is a counter to majority of melee toplaners, you will have hard times vs AD carries,they are simply a counter to juggernauts and that is that,make sure you time your E vs them.
RUNES: I am running attack speed quintessences,attack damage marks,armor seals and magic resist glyphs,the reason I take attack speed is because new Darius is all about getting Noxian Might, that's why his attack speed was nerfed like hell in the rework,so this will help you alot
MASTERIES: You have 2 good choices in my opinion those are Stormraiders and Grasp,you can look me up on LoLking if you want to see them,Stormraiders is good for movement speed and slow resistance always goes well with juggernauts,graps of the undying goes well with Darius passive but after they nerfed the heal I rarely use it,also you can try Courage of the Colosus
BUILD: Classic build:
I would recommend you try this build if you haven't already, if pretty much gives Darius all he needs,extra armor shred with
,
movement speed,
slow(very good when you E AD carries and give them an extra slow with this also crit reduction,
extra healing
Now it depends how the enemy team looks like,if they have majority AD consider buying
(and if you lane against
,
and other healing champions,also
is a monster item on Darius,it's been only seen as OP on
but this item is insane with Darius when you activate if around 3 enemy players,your HP is doubled and you can heal it all back with 1 Q if you have 
More offensive build:
since Darius has his early game nerfed a lot of times this build can change that,not only you get extra lethality with
you get more movement speed,add
to that and Stormraiders if makes Darius extremely mobile,other items I explained above.
Of course if you lane against AP you want to buy magic resist items right away after you finish
,if you lane against
buy
and so on.
If you have any question feel free to ask me or add me in game,also if you want to see my build on Darius with TriForce check it out: (haven't updated it for a while but it still stands good!) http://www.lolking.net/guides/390834