Jungle on him, it makes you a much more powerful presence in the game.
Ghost + Smite, no exceptions.
Grab Cloth Armor + 5 pots, head over to blue buff (hide near your turret until you see all 5 enemies on lanes so you know you won't get ganked). Put a level into Despair, turn it on, and attack the Golem. Once he hits you, hit your potion, and reapply it once it goes down. When he's around 50% health, smite him. Then just clear the rest of your jungle.
Once you grab your chain vest you can kill Dragon. You should be level 4-6 by now. Get your 2 buffs and go kill it, use bandage toss to stun it to reduce incoming damage. A health potion or two won't hurt. Once you're 6, gank every time your ult is up, otherwise stick to the jungle and keep farming.
Level order as follows:
W(Despair), E(Tantrum), W, Q (Toss), W, R (Ultimate), then prioritize R>W>E>Q.
Your item build should look like this:
Cloth Armor + 5 Pots
Mercs // Boots+3
[Another Sunfire or a Force of Nature]
You can grab Chalice at any point if your team needs Golem more than you do, but the Golem is really beneficial to you since it makes your ultimate CD much more manageable and lets you keep Despair on pretty much all the time.
Never use your ultimate to 1v1 past like 15 minutes in. Never use your ult on fewer than 3 players unless you can get both of their heavy damage dealers with it and your team is there to capitalize. Never run away if your team can have a numbers advantage after you die, those extra couple of seconds you're tanking could net your team another kill which sets them that much closer to an ace.
Also, be aware of enemy creep movement. If a creep wave is approaching, be careful with your bandage toss. It's a moderately long CD and far too useful to waste hitting a creep.