For those of you who do not know, Diana is an ability power based assassin/jungler. Her passive grants her 20% bonus attack speed as well as every third strike "cleaves" enemies, dealing bonus magic damage. Diana is one of the strongest junglers out there at this time. Her ultimate only has a 20 second cooldown even if it is not used with moonlight from her q. Her passive allows her to clear jungle camps quickly as well as apply things like red buff and malady's passive to all targets hit. She has great sustain if needed and is, in my opinion, currently the best burst damage assassin at this time.

Diana has quite the repertoire when it comes to skills. Her q allows her to shoot out two rays in an arc (crescent shaped) and any enemy hit is afflicted with moonlight. The moonlight reveals targets for a few seconds and has another effect when combined with her ultimate. Her w surrounds her with 3 orbs of light that explode upon impact, dealing some area damage. These orbs also grant her a shield that is refreshed if all 3 orbs are destroyed within a time frame. Diana's e is comparable to Darius's pull, however, her pull is slightly better. Darius has to pull in a line, whereas Diana pulls all nearby enemy units toward her. Any enemy pulled also suffers movement speed loss for a short time. The ultimate for Diana is an instant teleport to any enemy. It deals magic damage on impact, and when it is used on a target afflicted with moonlight, its 20 second cooldown (at level one) is instantly refreshed. With this skill list it is hard not to see why Diana is somewhat overpowered during ganks.

This part I get harassed on quite a bit. Diana's q is a great damage tool and all that, but I prefer to max the shield every chance possible (after getting q, e, and r to lvl 1 at least). This skill sequence has allowed me to hold turrets and get kills I definitely should not have... and still walk away from bleeding out, ignite, and poison. The shield is also a good tool while jungling because the less damage you take inside the jungle, the better off you are when ganking.

These can range depending on your personal choice and team composition, but I believe smite and flash are both musts. Diana has no escape tool without flash and it also grants her the ability to chase down targets for pre-6 ganks. Smite is a must because Diana cannot take out anything large without the true damage tool. Bonus gold is also nice for every smite use :)

I choose Magic pen marks because they give the biggest bonus throughout the game. Many people discuss how attack speed or ability power marks improve Diana's jungling, but I would rather be more useful during ganks and team fights that speed up my jungling minimally. The seals and glyphs are standard for junglers, flat armor seals and per level mr glyphs will give you a little extra sustain in any gank or team fight. The quints are definitely debatable, however, I am a huge fan or using the movement speed on quite a few different characters. Bonus movement speed allows you to catch runners or people that burn flash more easily than not. They also allow you to move to the gank spot more quickly and ravage the jungle faster.

These masteries are, in my mind, standard for Diana. The mana per level could be substituted for whatever else you see fit, but so far the 25/1/4 has not failed me. Diana is a burster, not a major fighter like Lee Sin or Xin Zhao.

Items are tough to make any call on. With Diana, I see rod of ages, merc treads and nashor's tooth all being necessities. ROA allows her to jungle without any problem after catalyst is purchased. Merc treads are simply a must. Any Diana that gets sorc boots or anything else will get crowd controlled in any fight and shut down immediately. The nashor's tooth allows her to proc her passive far more frequently as well as gives her a lot of cdr for her basic abilities.

This build is more of a glass cannon than anything else, but if you can get rylai's and roa you are more tanky than people think and can catch quite a few off guard with your shield. Tower hugging/diving is a great option as Diana as long as you can get your shield up and refreshed at the right times. If you feel the need to shut down someone like another Diana or Xin or any attack speed character really, just purchase Frozen Heart instead of malady and you're set. Abyssal scepter is also a good option for those AP heavy teams.

Blue -> wolves -> wraiths -> golems if you're gutsy -> gank top or bot even just to help push. Ganks are a necessary part of Diana's jungle route. If you don't try a pre-6 gank, you may end up with a team down 5 or more kills. Diana has the ability to gank lanes without her ultimate, you just have to plan and be prepared to maybe burn your flash for a kill instead of an escape. Flashing for a tower dive and first blood is definitely worth the 500 bonus gold to me, but you may think differently...
Counter jungling is not truly an option with this build unless you are beating your opponent's jungler pretty badly. 1v1 jungle situations are pretty easy to handle, but if you are to get caught in a 2v1 your likelihood of survival goes down to... maybe 10%.
Diana has great creeping ability once nashor's tooth is in your item stack. When someone needs a lane covered, take the creeps because you need the cash. With Diana you have the power to out creep and out level mid or solo top if you perform well. You can also have ROA by 15 minutes or so if you land first blood and a few kills after.

Diana can hold the front line, but I always prefer to flank the enemy and rush in with q hitting their carry and dashing in with a shield. Diana's pull is the most op thing for a team fight. You can pull an entire enemy team within tower range or back toward your team mates if you're running and will die anyway. Diana's job varies depending on the team compositions, but she fits any role the team needs in a fight.

I think Diana is simply awesome. She rivals my Lee Sin in sustainability and fighter style play, but she has far more burst than any character I know. I hope you enjoyed this guide and maybe will throw some suggestions into your comments. There's always room for improvement and the winners of games are usually those who adapt instead of see one play style or build being their only option. So long as you can be flexible, Diana is a ridiculously amazing choice for a jungler.