Not Updated For Current Season
Warmog's Armor against mixed damage comp.
Zephir against targets with a lot of mobility.
Zz'rot Portal and Ravenous Hydra for splitpushing.
Spirit Visage against a team with a lot of magic damage or against a fed APC.
The Bloodthirster for ToD (Tons of Damage).
What you need to do
It is very easy in theory.
Until you buy BotRK play pasively, farm and harass with Q.
After that go all-in, you have enough CC to stick to your target and kill it.