Most runners including me were using Yi for completing the tutorial but Darius is better

Here's a simple guide.

• After you pick him, atack the second minion and go for a Q. The reason for that is that when you just go for Q this minion simply ignores you and after you kill Vel'Koz he stops your wave from crashing with you in the turret, which might lose 1 to 2 seconds
• Tank the turret and go for a clear wave with your Q hitting Yasuo. Hitting him helps your team kill him instantly after they spawn and your minion wave will not slow down. Don't waste your ultimate there, I'll explain later.
• You can tank both tier 3 and 2 turret
• You must to take down tier 3 before the inib fight. By the time the inib fight is about to brake, if you ulted Yasuo, you'll not be able to ult Jinx as soon as she apears because your ult would have ran out.
• At the inib fighy kill Jinx with your ult and get the passive.
• Hit Braum before the passive ends and ult him before he dies to keep your ult up for the final part. Note: if Sion clears your minion wave with his ult, just restart. It happens very often so try to bait him, standing somewhere he will not clear it completly
• Take down the nexus turrets, you can tank 1 of them but be carefull to not die.
• When the nexus is exposed a fight will brake, do not get hit by any knock up, or you'll get ulted by Yasuo.
• Ult Sion to proc your passive, but don't use your W on him.
• After killing him just take down the nexus, you should be able to use W twice with your passive.

This strat proved to be more effective than Yi's one, but it's less consistent... So you'll probably get lot's of bad runs. Also Darius involves more variables than Yi, the faster yi (to date) just ignored the enemys and focus the objectives. As Darius you have to be way more active. Good luck

Trick to upgrade your abilities: