Kayle is a jarring champ to start playing if you play traditional mid laners because she only has 2 ranged spells, and early game they're very weak and until level 6+, You're a melee champ. Play safe on kayle, There's very few champions you can actually fight pre 6. Bide your time & wait for mid-late game.

Good! You should be on your Nashor's tooth and berserk's grieves as well as being on your way to rift maker. Now that you're level 6+ you can start to farm a bit safer against ranged champs and assassins, and you don't have to let every wave hit your turret, although in some matchups you still might want too. With the power you now have in your ultimate you can start to roam with your jungler and secure objectives.

You made it! You're on 3-4 items! At this point the game is all but guaranteed. As long as you protect yourself and your teammates with your ultimate and use your commanding damage and presence on the map to secure neutral objectives for your team, it's very easy to close out a game on Kayle, just be careful not to ult too late!