Kayle wants attack speed and on-hit damage. Your power comes in the late game.
In general, Ghost is a solid Summoner Spell in ARAM. Depending on what Summoner Spells your teammates take, you can also opt for Cleanse (anticipating CC on the enemy team, and there is a lack of frontline/tanks on your team) or Exhaust (anticipating assassins on the enemy team, and there is a lack of carries on your team).
General Power Spikes
Weak: Level 1 - Level 5
Average: Level 6 - Level 15
Strong: Level 16 - Level 18
How to Play
Early Game: Play safe. You want to soak as much XP and gold as you can. Your objective should be to minimize losses rather than maximize your gains.
Mid Game: Once you have built a couple items, and have 1-2 points in your R, you can start to look for poke and team fights. Be careful not to overextend, as you are still significantly weaker than you will be late game.
Late Game: You should focus front to back during team fights and attempt to use your R on teammates during fights when possible (obviously save yourself if needed). You out scale most all champions between Level 16 and Level 18, so play aggressively and be willing to challenge to get a spawn advantage.
