Greetings,

I'm DeadFaith, a new player to the League on the EUW server.
Ever since i saw Sp4zies video of him playing Diana, I wanted to try her out. The very next week, she was in the free champion rotation, and some time after that, she was on sale, so i grabbed her and her Lunar Goddess skin cause it's just too crisp.
I'm here to share the build I currently use on Diana when jungling.
Since Dianas passive makes her every 3rd auto-attack deal tonnes of damage, I thought to focus on making her AA's really strong while still keeping her signature burst, and this abomination is what I came up with.

Since I only have 2 rune pages, my personal choice for the runes is the following:
9x Flat AP Marks
9x Flat Armor Seals
9x Scaling Magic Resist Glyphs
3x Flat AP Quints

Gives nice early damage, solid sustain and overall feels pretty good on her.
An alternative is to replace your Flat AP Marks with Flat Magic Pen Marks.

When putting this build together, I focused on massive attack speed. Thats where Nashor's Tooth, Guinsoo's Rageblade and Stalker's Blade - Devourer come into play. Devourer early game will boost the output of your auto-attacks substantially, but when you get it make sure to clear out jungle camps as often as possible until you sate it for max damage output.
After completing Devourer and getting Boots, focus on getting Guinsoo's Rageblade to boost your DPS through the roof and leaving your opps in shock.
After that get your Berserker's Greaves and Nashor's Tooth for even more attack speed and more passive 3rd auto-attacks. There is also that crisp passive from Nashor's for even more damage, that is influenced by Devourer!
In the lategame you want to get some sustain, so thats where you can chose what to build first: Zhonya's Hourglass or Hextech Gunblade. If youre doing well and not dying, you can go for Gunblade first as it will give nice sustain through spell vamp and life steal and give a nice bit of damage to both your auto-attacks and your abilities. If you notice youre dying a bit or are behind in towers and objectives, go for Zhonya's. The armor will mitigate the physical damage and the passive will likely save your life in clutch situations.

First ability is your Q, as it gives you sustain and damage while clearing camps. After that comes your awesome curved skillshot, Q, which you will use to introduce yourself to the jungle camps and future victims. I level my E lvl 3, mainly to get some cc if I get counter-jungle'd or if I go for the Scuttler, which loses majority of his armor and magic resist if you slow him with your E. After that, max your Q, followed by your w and lastly e. Level your R on lvls 6, 11 and 16.

Not a lot to say here, just standard jungler spells. There are some alternatives:

1. - Smite and Ignite are sometimes used in the jungle, but i dont feel Ignite is exactly the spell to take on Diana in jungle. You can use it if you are super confident in winning.

2. - Teleport and Smite - several gold-diamond friends of mine suggested to take teleport over flash, as the item build makes for a good split pusher.

Here is my usual jungle route:
Start at Krugs using your smite, as the passive stun every 6 basic attacks does a lot in sustaining you, proceed to Raptors, followed by the scuttler. decide whether or not you'll gank bot. when your smite is back up go to the red, smite it for true damage, and cross to the ''blue side'' of the jungle. kill the wolves, gromp and then smite the blue. kill the scuttler to regain some hp and mana, and then decide if you should or not gank mid or top lane. after that go B to get your devourer

you will be very close to being an AFK jungler in the early game, as Diana is a weak early game champ. you want to farm your jungle until you get your devourer and guinsoo, gank if you think you can get a kill somewhere. in the midgame, when you get your lvl 6 and ult, you get your first powerspike. if, by that time, you have some damage items you can gank and probably get a kill or assist.

lategame your main combo is:

prepare 2 stacks of
+ + + + +

versus tanky opponents you dont use your 2nd R, instead you auto-attack them, with your Guinsoo's Rageblade and Stalker's Blade - Devourer you will outdamage them, and with Hextech Gunblade you will outsustain them as well.

In teamfights, you will take the role of an assassin, focusing opponents ADC and mage first. If you still have your cooldowns you can easily take on another tank, while you have Zhonya's Hourglass as a life saver.