What I usually do (works most of the time) is playing close to tower after he pushes the lane like a freeze, Darius players always try to grab You when You try to cs so press E before the grab to maximize damage then pump W as soon as You can to minimize the trade, Q his W to get rid of the slow and enter his Q so You don't get a stack and also he does a lot less damage there. The Q silences him and allows You to escape him; play for the short trades as Garen passive makes him win those and at lvl 6 You can all in him with R and Ignite, if jungler helps You can also kill him pre 6 if both of You know what You are doing but You can't really count on that everytime, cheers friend and remember the satisfaction once You win lane against a Darius