First: Dont get creeping death. The armor mace of spades gives increases with the damage you are dealing. So getting a Bloodthirster, then hitting 1 guy will give you around 50-70% armor. Get it after you max mace and siphon. Mace and Siphon give you more shield and seriously rape creeps. Which is good for your Bloodthirster.
I seriously love stacking Bloodthirsters on him. It is very very easy to stack because of his awesome farming skills and unharassable-ness. I find myself getting one B.F. Sword at level 3-5. That alone makes you a force to be reckoned with. With the BF sword, you can rape Lizard Elder that early alone. And then with the crest, you can proceed to rape enemy champs.
Then I check which boots I need. Against Casters/Mass CC - Mercury. Anyone else -> Swiftness. Swiftness rocks on him because he has a lot of difficulty closing in on a champ and the extra movespeed helps alot.
Then after finishing my first bloodthirster, I check on what I need.
Enemies escaping too much? Need some HP? Even matched fight so far? Get Phage, Atmas then to Frozen Mallet later on. An awesome thing to note: Phage AND Lizard elderworks with your ghost slave. So if you need a slow but you cant do it your self, then send your slave over for the kill.
Pubstomp much? Stack as much Bloodthirsters as you can. One game, I got to 4 Blood thirsters. I had like, 480 damage per hit with over 100% life steal AFAIK.