Diana... Diana... Diana. Oh my. Fallen from grace, saved by the moon. I love her. I love every little thing about here. You can either play her as sustain, as burster or as bruiser. I think she's most viable in the jungle, since her Moonsilver Blade makes her a very quick jungler and her Crescent Strike makes her ganks incredibly efficient and powerful.

I chose these runes, because these are my standard caster runes. They give you enough ability power and magic penetration to be ganking at level 3 to 4.

The masteries are straight forward destruction / jungle. More damage on jungle minions, more damage on champions. One might consider putting more points into utility and increase the duration of buffs, but as I play Diana more and more, I think it's not necessary. She's fast as lightning with jungleing, and I tried invading against Volibear, Fiddlesticks and Shen, all three died to me at level 6. Just make sure you activate your Pale Cascade after you hit with Crescent Strike and before dashing in with Lunar Rush. This keeps you healthy and full of mana, even without Runic Affinity .

The items I proposed are more or less standard caster items. I like getting my Sorcererc's Boots early on, because they give my Moonsilver Blade an advantage. I don't think that Mercury Treads are a better choice, since I go for the kill and play Diana as an assassine. Mercury Treads would give me some magic resistance, but my whole build is for killing and taking down champs, and not sustaining for long.

Hextech Revolver into Will of the Ancients will provide you with the needed spell vamp. Alternatively, you can get a Hextech Gunblade. This ought to keep you healthy in the jungle.

Your primary damage tool is Crescent Strike combined with Lunar Rush. Don't just double dash and kill (although the cooldown on Lunar Rush is ridicously low), sustain. Hit your target with Crescent Strike, dash in with Lunar Rush, trigger Pale Cascade and pull 'em back in with Moonfall. That will bring the target down to about 20% health. By that time, your Crescent Strike will (should) be off cooldown, and you can hit again with it. The finisher is Lunar Rush. Don't be afraid of diving a tower with this combo. It's easy to land a kill this way, and run / Flash out again afterwards. The only time, where you can't do this from level 6 on, is if the support or the target has a stun, snare or knock-up.

In teamfights, try to land the Crescent Strike again and again. If a target is low on health, dash in ( Lunar Rush), trigger Pale Cascade, kill it, and flash away.

My jungle route is pretty straight forward. Since Diana has insane amounts of damage, with Crescent Strike, Pale Cascade and Moonfall, I go Blue, Wolves, Wraiths, Golems and Gank bot or top.

This build is not yet complete, and I'm working on it. It takes some time to try and get used to Diana.