How to Darius?

Ok, I have to confess: I'm Mastery Level 5 with Darius and have been so since season 7. Yet after getting 180k mastery points, I still cannot get an S- or higher on him again. I even got a level 6 Illaoi recently, a champ I had given up on pre-rune rework.

So, Darius mains who have had some luck with Mastery leveling, any tips for getting Mastery 6 and 7 without afk farming/pushing (or in other words in the teamfight when it happens)? I'm open to everything: preferred bans, rune setups, itemization priority, ability priority and laning or teamfight strategy mostly though.