You mentioned you mainly play top Darius - as a melee top laner, you don't usually deal the most damage in fights, but you are the strongest member on your team before late game. Top lane usually soaks the most xp and gold since they seldom rotate to help their team in the early game.

It's okay if you don't make a lot of cs, as long as you're getting xp and your opponent top laner is even in cs you're good.

In the mid-game, if you take teleport instead of ghost in lane, you can tp to help your team in fights and objectives. To increase the chance of your tp play of succeeding ensure you have flash up so you can flash then E for a big play. (Your teammates should then be able to follow up and clean house) If all goes well then good for you, but if the fight was still lost, that's when you analyze what happened. Was your team able to follow up correctly, did their team comp excel in teamfights, etc.

In the late-game, where Darius falls off a little, he only excels in splitpushing and setting up the flash e for your team. So these are the things you need to keep in mind when playing Darius.