OVERVIEW: since you're familiar with Diana, familiar with the playstyle and itemization, you could play Diana jungle. the rune setup, masteries, and itemization that you choose all depend on if you want to build a more tanky diana, a diana that does more burst damage, or more AP heavy.
diana is a pretty strong jungler, clear time is fairly fast, she does a lot of burst damage, only downfall is that because she doesnt have a gap closer until level 6, you have to rely on great positioning and using your E (moonfall) to get off early game ganks.
rune setup 1:
9x attack speed marks
9x armor seals
9x mr/level glyphs
9x AP quints
attack speed marks are for the fast jungle clears, flat armor for jungling, mr scaling so you scale better into the late game, and flat AP quints so you can clear early jungle camps.
rune setup 2:
9x magic pen marks
9x armor seals
9x mr/level gylphs
9x AP quints
only difference is the magic pen marks instead of attack speed. jungle clear time isnt as fast, but deal more damage and scale better into mid/late game with the magic penetration.
mastery setup 1:
9-21-0 - tanky setup with some AP/magic pen, with 21 points into defense for a more tanky build, better sustain, and easier jungling
mastery setup 2:
21-9-0 - AP heavy build with 9 points into defense for health and tough skin
mastery setup 3:
9-12-9 - magic pen, health tough skin, mana, runic affinity - a more all around build where you get the AP/magic pen, you get the health and armor, as well as the mana regen and runic affinity for jungle buffs.
start off with a point in W, max Q first, only one point in E at level 4, then max W second.
W, Q, Q, E, Q, R, etc..
when you initiate a fight, start off with W (pale cascade shield), then Q (crescent strike) on them, R (lunar rush) onto them, then E (moonfall) when they start to run away, then R (lunar rush) again to close the gap.
there are two main jungling paths that you can take as diana
1. aggressive, quick level 3 gank -
skill order: W - Q - E (quick point into moonfall so you can close the gap and hopefully kill with the gap closer and red buff)
start wolves -> blue buff (smiteless leash) -> small wraiths -> red buff (smite)
you hit level 3 after the red buff, still have 2-3 pots left, and are able to get off a quick gank at level 3
2. passive, level 4 gank:
skill order: W - Q - Q- E
start wolves - blue buff (smite) - small wraiths -> big golems -> red buff (smite) -> small wraiths
you hit level 4 after this path, have 1-2 pots left, have two points into Q (crescent strike) and can do damage!!
-always start machete, 5 pots
-first back, try and get 850 gold, so you can get boots and spirit stone
-you can get some early game doran rings (at most 2, for early mana regen, AP, and health for jungle clear)
-upgrade spirit stone into spirit of the spectral wraith for the AP,CDR, spellvamp sustain
-sorcerer boots for the magic pen, deal more damage, as well as run faster for easier ganks
-by the time you get sorc boots and the spectral wraith (only real item difference between a mid diana/jungle diana), you can build diana like any other AP mid diana.
-if the opponents team is more AP heavy: pick up Abyssal Scepter for the MR and MR reduction
-if the opponents team is more AD heavy: zhonya for the armor and zhonya sustain
-if your team needs more damage: rabadon deathcap or liandry's torment for the AP/magic pen
-if your team needs more sustain/tanky: aegis for the armor, MR, and damage buffs
If you have any questions about jungling, feel free to add me in game and I would be more than happy to help you with anything ya' need!