Earthshaker is a melee strength support hero famed for his ability to stun from extremely long range with his impassable Fissure, and for his ability to potentially completely turn the tide of a fight with his ultimate, Echo Slam, providing the situation is just right.
Skills
Fissure is skilled and maxed first.
Enchant Totem is skills and maxed last.
Aftershock is skilled and maxed second.
Echo Slam is skilled at every available opportunity (levels 6, 11 and 16).
Early-Game Combo: Fissure > Enchant Totem near the enemy (with Aftershock taking effect) > Attack.
Mid-Game Combo: Enchant Totem > Blink > Echo Slam > Attack > Enchant Totem or Fissure > Attack > Enchant Totem or Fissure > Attack.
Items
Starting Items: Courier and/or Observer Wards, a set of Tangos, a Healing Salve, 2x Iron Branches, 2x Clarities.
Early Game: Flying Courier, Osberver Wards, Boots of Speed, Magic Wand.
Core Items: Observer Wards, Arcane Boots, Blink Dagger.
Luxury Items: Aghanim's Scepter, Drums of Endurance, Veil of Discord, Shiva's Guard, Refresher Orb.
Situational Items: Smoke of Deceit (ganking), Dust of Appearance, Sentry Wards, Gem of True Sight (vision), Soul Ring, Bracer (early game), Heaven's Halberd (late-game anti-carry).