This hybrid Diana guide should help. If it doesn't email me at overdouse@gmail.com. Let me know if you have any other comments or corrections. Hope it helps!
This guide is mainly AP, due to obvious reasons of all skills(including passive) are ap based.
This guide is for only people INTERESTED IN PLAYING DIANA!!!but if your just browsing to make grammer corrections GTFO.

PROS: CONS:
great passive - not a lot of cc
high dmg output - not good at escaping
long range ulti/Q - not very tanky
good gap closer - not very good against tanks
quick at taking out minion waves - runs out of mana quickly early game
great AOE dmg - not the best sustain
early and mid game dominance
low cooldowns

For summoner spells I take Flash and Ignite. I use flash because she doesn't really have an escape skill unless there's a minion toward your turret. So I take flash to get to my Turret and be a troll and harass as much as possible with Crescent Strike (Q). I take Ignite to finish off my opponent without turret diving or trying to get passed other enemy champions. It secures my kill with out dying per-say.

Diana does not exel at late game as much as other champions, her strong suit is early and mid game. which is why she needs to dominate then, and get the largest advantage possible. This is why I took flat ability power for early game. Diana has low cool downs so why giver even more cool down reduction? well her ult has a reset but only if they are affected by her Q, so if you reduce the cool down on her Q you can use her ult three times and her q twice with in the span of about 3.5 seconds so I took cool down masteries and runes. I took armor and magic pen masteries because she needs help facing tanks so I added that to void staff/last whisper and sorcerers shoes. I took dmg and ability power for level basically only for dmg output through out the game. Diana has great bust dmg but she needs something to help her secure the kill thats were her passive and executioner come it to make sure that she puts out the maximum amount of dmg as quick as possible. the defensive masteries are for early game sustain and early game gameplay in general.

Glyphs - cool down reduction) again, this is so you can use her Q and R as much as possible in a short amount of time.
Quintessence - AP per level) this is to give her some help with late game.
Seals - flat armor) she has weak sustain so she needs an armor boost.
Marks - flat AP) for early game domination.

I start off with the typical start of boots of speed and three health pots. Then I start to build late game items(sheen,phage,bligewater cutlass.) and then get a cheap mid-late game item in this case Nashors Tooth, Then jump into Trinity Force followed by Hex Tech Gunblade. Now you need sustain so I pick up Rylai's for health and cc, and finish with void staff/last whisper. Hint: if your facing a fed team consider getting void staff/last whisper earlier, like after Nashors Tooth.

I put Cresent Strike first because its her main dmg and skill shot. You can check a bushes well because it shows them for 3 seconds. Upgrade Cresent Strike as soon as possible after u get your W and E.Next is Pale Cascade (W). Its three orbiting spheres that explode on impact. If all of them explode she gets an additional shield. After Pale Cascade you should get moonfall (E)) that you should upgrade fully last. Take it a level 3 then don't up grade it until every thing else is upgraded fully. Last but not least is Lunar Rush (R). Get that one at level 6,11,and 16 like all other ulti's.

When your farming with Diana you use Moonfall (E), then you use Pale Cascade (W), followed by her Cresent Strike (Q) than passive, and ulti is needed for super minions, and all are AOE.

Team Fights:
When you're team fighting be sure to engage with Crescent Strike followed by Lunar Rush then Pale Cascade and when your opponent starts to run use Moonfall. With that combo it's guaranteed to help your team in team fights.
Ganking:
When you gank with Diana make sure u land crescent Strike before u use your ult because when moonlight ,the passive of Crescent Strike, is on the enemy her ult doesn't have a cool down. And again when they start to run use Diana's E. you will usually get the kill or kills when you use that pro ganking strategy.

This guide is for Hybrid Diana only. Hope it was useful and enjoyed it!