This build should be able to give you a good idea of tips on how to play Darius as a Team Fighting Top Lane Tank DPS. Try to follow the build as much as possible but do make some comments on what i can improve on.

Take 21/8/1
Getting mostly Armor Pen with some Attack Speed and Attack Damage in Offence and getting Armor with Health Regen in Defense, get Improved Recall Or take a point into Bladed Armor.

You want to start the game with boots of speed & 5x Hp pot OR with a Regrowth Pendant & 1x Hp pot. Then try and get a GP5 item, preferably Heart of Gold for health or Philosopher's Stone for regen. After getting you'r GP5 you either want to rush a Frozen mallet or Bloodthirstier (while building into boots that you need) Take Maw of Malmortius if they have high AP damage and take Atma's Impaler if they have high AD damage. Finally Build into either more offence or more defense, for going offensively get Phantom Dancer and/or Infinity Edge, for defense take Force of Nature and/or Thornmail.

You will most likely want to max your Q out first with your W same lv as E on a normal game, if they build heavy armor max E instead of W but if you want to burst them faster max W instead of E

Take Flash and Ignite for your main summoner spells, if that doesn't work swap either Ignite for Exhaust or Flash for Exhaust, Use ignite with your passive and ultimate to finish off a primary target, if you have exhaust use it on the ADC to shut him down and get him killed. Flash should be more used as a escape tool rather then a chase tool, Darius and 2 chasing spells, but flash is you'r one escape tool so don't use it to chase often (do use it if you must and wont need it for a while)

When in a team fight you want to try and pull their ADC into the middle of the fight so your team can focus him down, Spam Q when its up and try to stick to one target, don't go running around looking for someone to dunk you want to be with your team so you can win teamfights. If you can catch one of them out of position try and kill them with out getting re-payed badly in a 3 for 1 exchange.