My in-game name is luffy18 and i'm a gold 2 player right now(former platinum 3 in season 5).I main a large variety of champions but my most preferred ones are assassins.Diana is a great assassin with a lot of burst and sustained damage.After reading this guide you should be able to learn pretty much everything there is to Diana.

The standard AP rune page is okay for Diana.After you play a dozens of games with diana you can adjust you page a little,by this i mean you can swap mr blues for ap blues if you feel you don't need the mr for example,but in my opinion it doesn't make mch of a difference if you play your champion right.Runes are mostly to help your early game.

Pretty much the standar 12/18/0 page for assassins.I wouldn't change anything here.Diana is an assassin and should be played as one.Bruiser or tanky Diana is not that good as she is not tanky enough for a tank and doesn;t have any sustain.