
Pudge is one of the strongest gankers in Dota 2, and the most popular hero in the game. He usually lanes mid, in order to acquire a fast level 6, then goes ganking with his combo.
Your combo is Meat Hook > toggle Rot as the enemy travels back > Dismember.
Skills
Get a point in Rot first, then focus on maxing Meat Hook.
Get Dismember whenever you can, then max Rot.
Max Flesh Heap last - it's retroactive so you'll get all of your flesh stacks when you eventually level it anyway.
Go ganking as soon as you hit level 6/7, or kill the enemy hero mid.
Items
Core: Bottle, Boots of Speed (upgrade to Power Treads or Phase Boots), Wand or Urn of Shadows.
Post-Core: Blink Dagger or Force Staff, Aghanim's Scepter.
Luxury: Heart of Tarrasque, Assault Cuirass, Shiva's Guard.
Situational: Pipe of Insight, Drums of Endurance, Vanguard, Ghost Scepter, Black King Bar, Crimson Guard.