There are two different ways I like to play the hero. Either as a spell caster or a right clicker. Based on the other 9 players in the game you should make a judgment call to decide what playstyle works for you!

Skill build: Max Shadow Strike first if your enemy stays in lane with you. If your enemy is clearing waves then max Scream of Pain so you can clear waves and farm faster.

Items Spell Caster: Eul's Scepter of Divinity, Aghanim's Scepter, Scythe of Vyse

Items Physical Damage: Orchid Malevolence, Maelstrom, Black King Bar. Upgrade to Bloodthorn and Mjollnir.