Diana is an AP melee jungle, which can have a really high burst with small items.
She's a really quick jungler and got great gank potential, with her Ultimate + E Spell.

Start up with Boots and 3x Health Potion
Try to get Heart of Gold philosopher's stone and kage's lucky pick fast.
Rush for Mercury's Treads after to be faster when ganking and avoid the cc from lanes or the enemy jungler.
Now you have 2ways to go, Tank or Burst. I prefer the tanky way, because you still have a decent amount of damage and you can engage perfectly without droping instant.

Rushing Rylai's Crystal Scepter is a good choice. You can gank really good, because you can slow with your q and burst with Lunar Rush + Pale Cascade

If you play against a most likely AD-team, you go for Frozen Heart after rylais. It makes you incredibly tanky and gives you a good amount of cdr which is helping you to burst carrys down.
If you play against an AP depended team, go for Abyssal Mask. The reason should be obvious.

I go for Deathfire Grasp after frozen heart or abyssal to have an incredibly high burst against carrys.
If you went frozen heart first, get an abyssal after your dfg. If you went abyssal first, get an frozenheart now.

It depens on your last item. I would go for Guardian Angel most of the time to be even more tanky. But, you can also go for:
Lich Bane if you need more burst
Randuin's Omen to reduce more attackspeed, and be more adorable against AD's
Banshee's Veil go have more tankyness against AP's
Zhonya's Hourglass sometimes it's a good choice aswell. But i never use it.

Quintessences:
Greater Quintessence of Ability Power for some early damage

Marks:
Greater Mark of Attack Speed you will have your passive up faster, and so you can clear junglecamps much faster

Seals:
Greater Seal of Armor to survive in the jungle

Glyphs:
Greater Glyph of Scaling Ability Power gives you the decent amount of damage you need in lategame.

Going 9/12/9 may be confusing you, but the reason is simple:
9 in offense gives you good damage for clearing jungle and doing some early ganks.
12 in defense will help you to clear the jungle faster and saver
I take 9 points in utility to be a bit faster when ganking and because of the 10% buffholding ofc.

Flash Best Escape skill. Good for chasing aswell.
Smite Obviously needed when jungling
Ignite Diana needs her flash to burst some people down sometimes, and to escape.
Exhaust Same explanation as i used for ignite.

Crescent Strike (Q): Important skill for chasing people and bursting people down. Helps you getting kills if good used.
Pale Cascade (W): Well, i max it first because of the incredible damage it does when ganking, and it gives you a really good shield.
Moonfall (E): Explains itself. It pulls all enemys to you and slows them.
Lunar Rush (R): Perfect gapcloser, and high damage.

PROS:
- High burst with small items
- Good sustain in jungle, with her shield
- Perfect carrykiller
- Good ganks
- Pretty tanky


CONS:
- No Escape
- Can get kited pretty easy

Wolves -> Ancient Golem -> Wraiths -> Lizard Elder -> Mini Golems -> Wolves -> Wraiths -> Shop -> Gank Top -> Gank Mid


After that route you should normally have your Philosopher's Stone, if there are no issues while you are jungling.
Ganking Top is very easy with Diana because you can easily go around the tribush and just pull the enemy into you and your teammate with Moonfall. It's the same thing with the Midlane.
Ganking Botlane is a bit more difficult with Diana, because she is to slow to just come around when its warded. The easiest way to gank botlane is, telling your botlane to push and just do a ninjagank.

Your job in the lategame is to focus the carry's. You need to jump on the carrys immediatly when starting a fight. The reason why Diana has to do it, is simple. Diana got an easy 100 to 0 Burst with Crescent Strike + Lunar Rush + Deathfire Grasp + Pale Cascade + Lunar Rush.
You can do this even more easy, when u have your Guardian Angel, because you won't drop instant if the tanks try to defend their carrys.

All in All Diana is a kinda strong jungler.
She has great gankpotential, high burst and doesn't fall off in lategame.
She has some points to critize(She doesn't have good mobilty, for example) but thats not a big deal in my opinion.
I loved to play her since she was released, because her mechanics are really fun to play imo.

I hope this guide may help you playing Diana.
Comment & Rate please.

Peace.