Well, depends on how you build her, DPS or AP. I prefer AP, since she is a terrible DPS. Going AP allows two things, way more damage with your Q, for last hits when they run, and it adds damage to your E.
For farming, you should start off with E, that way you can last hit from a distance, and since it's AoE, you can damage other minions, getting ready to last hit.
Here is THE best AP build out their for Kayle. It's a mix of AP/DPS. Giving you about 300-500 AP at end game, and 1.5 Attack speed.
At the item build, I advise you to follow the one that says Ideal build( Mage/DPS)
Good luck, and have fun with Kayle