Whether I'm using Ooze or Bestial Wrath, I almost always follow this build:
1: Venom Spit. the skill no UB should ever leave home without.
2: Inner Beast: upgrades your most important stats.
3: Diseased Claws: 5% is ok. I doubted at first, but you really need to catch up to kill
4: Venom Spit II
5: Post Mortem. your best creep killer, usually gets me lv6 faster.
6: Inner Beast II
7: Venom Spit III
8: Foul Grasp: helps stop the big pots and tele scrolls, netting you kills at times.
9: Inner Beast III
10: Venom Spit IV
With those as a base, you'll want to harass and keep harassing all day long. Close up, spit, run, close up, spit, run. If you get em far enough from their towers go for the kill. Keep always an hp pot for these opportunities. I find that Wyrmskin Handguards help to slow them down enough to kill em. Otherwise AVOID GREED LIKE HELL, better safe than sorry, you don't wanna feed gold and exp. Once you hit the higher levels of Venom Spit, you'll become very dangerous, maybe not because of net kills, but you'll make people turn around to heal and you'll gain ground. I usually don't bother spitting towers until Venom Spit III, but 2 is ok if they don't buy regen.
As far as Favour Items go, I use Swift Anklet, but I'll give Blade of the Serpent a try (I bring combat mana pots). Furious Blade however is what you want to aim for when u get the favour. The amulet of teleportation is neat on those big maps. Helps u catch the first two flags fast.
For starting equips, Banded Armour or Gauntlets of Brutality is the usual (along with pot and tele scroll). Since I'm not gonna be doing much of auto-attacking, I get the Boots of Speed, because you'll be doing a lot of running. Then I go for Wyrmskin Handguard to see if I get lucky and get a kill (usually do in 1v1 against unsuspecting fella without a pot). Next item on the list is the Slayer's Wraps, neat little item with crit, atk and regen, all good for you. Then I get a Heart of Life. Great to harass.
Then you wanna know what you want to do by lvl 10+. I usually head for Ooze because there's a lot of ways around Bestial Wrath. Wrath however is great to kill unprotected towers along with Spit. If you got say 2 tammates working one lane and you always meet 1v1s and so, sometimes I go for Wrath to flank to their portals.
Anyway, for Ooze builds, I go like this:
11: Ooze: I always leave Ooze for later when I can afford the regen
12: Ooze
13: Ooze
14: Ooze
15: Putrid Flow: It's amazing really, it can turn a game around with Ooze. Suddenly staying close is a pain in the ass.
16: Acclimation/Plague: Get acclimation against Snipe Regulus, TB, Hammer Rooks and Pouncing Sednas.
17: Plague/Enhanced Attributes: Plague is a b**** if they rely on Heart of Life, plus a small DPS source.
18: Enhanced Attributes
19: Enhanced Attributes
20: Enhanced Attributes
I follow with Heart of Life (+15) then Platemail of the Crusader (+20 and armor) and Narmoth's Ring (+20 and drain). That's usually enough to hold for Artifacts (Mage Slayer, Cloak of Elfinkind, Ashkandor...). Btw, Bulwark of Ages also reduces the damage you take from Ooze IV to 38. Of course, if you had to buy Citadel upgrades and you had to delay regen stuff, be careful when using Ooze.
Difficult matches can be those who negate Venom Spit: Oak with Shield, QoT with Bramble Shield, Sedna and Erebus with Mist. They will however go down if you push them hard enough. At least with the first three they'll use up their mana. Tower Rook can also be a real pain because all you can do is Spit before losing most of your health.