The easiest way to Get Stardust in Pokemon GO is through catching Pokémon.
Each time you catch a Pokemon, you'll be awarded 100 Stardust and three Pokemon Candy.
Each time you hatch an egg, you're awarded with Stardust, Pokemon Candy and XP.
The amount of Stardust you'll receive depends on 2km, 5km, or 10km to hatch the egg.
By defending Gyms in Pokémon Go, you can earn a significant amount of Stardust.