I jungle as Diana and I found that you need the Tough Skin and Insight mastery from the Resolve tree for maximum effectiveness early on.
Despite Diana being AP, I still started with Hunter's Machete as I personally found the Hunter's pot to be absolutely terrible. You either get Hunter's Machete + 3 pots (450 health) or Hunter's potion alone. Plus Hunter's potion doesn't build into any jungle item.
I think Riot really wanted junglers to pick into the Resolve tree instead of Cunning. Now, you either have to choose between Tough Skin, Insight, Vet Scars or Savagery, Merciless, and Dangerous Game.
Also, it helps to get Double Edged Sword on melee champs like Diana and I found the extra damage helps a lot.
My mastery page for Diana: http://puu.sh/llLeM.jpg
Runes: 9x AS marks, 9x Armor marks, 6x CDR/level glyphs + 3x AP glyphs, 3x AP quints
Start: Krugs (smite), Razorbeaks, Red (smite), Blue/Scuttle