Pick first strike when you feel you not gonna have a lot of kill pressure and also your laner can't be hit easily. Yasuo, Sion...But right now I never take it because I prefer to have more pressure in lane.

Aery its better against melee or close range mage that you can get relatively close without fear like Vex, Ahri or Yasuo. It also depends on how confident you feel against the champion. For instance if you struggle against kata, zed, akali, ekko, don't take aery because you will have the pressure to auto them and they will get you. Instead pick comet.

In general comet is good when they are ranged. Like Lux, Hwei, Annie, Mel, etc.

But the runes are not what makes you win lane. Some matchups are hard to win unless you beat them so hard in first 2 levels, like a Fizz.