How Should I Play Darius?

Don't play him. At all.

These are all solid items on darius.

With darius, you generally want to play aggressively early(Ward so you do not get destroyed by a gank), and punish the enemy opponent for trying to CS with your Q. When the enemy falls below about 50% HP, you can really start zoning, and punishing much harder for mis plays. If they have mobility, wait to use your E, and always make sure to use your E and W in tandem.

Late game, you HAVE to flank unless you have a lot of hard engage. The issue with Darius is that he is not very hard to kite, and while he can be hard as hell to kill, he has to walk at you to do damage, so coming in behind them is an extremely good way to make up for your lack of engage, as your team can collapse as they come for you, or you get to the fight as it starts and have a hay day, as flanking with generally put you straight into their back line.

I wish i could give more, but I am not the best Darius, and I do not want to tell something that will fail you.

Well I'm not a total pro, but one thing you should know is never go against someone who can kite (Jinx for example). That's how Darius dies.

EDIT: Now don't go against someone who can kite if they are good with that champ. Bad Jinx's and other ones can get slaughtered by Dariuses.