You can get Lapis Lazuli via breaking blocks of [Lapis Lazuli Ore](https://minecraft.gamepedia.com/g00/Lapis_Lazuli_Ore?i10c.encReferrer=aHR0cHM6Ly93d3cuZ29vZ2xlLnJ1Lw%3D%3D&i10c.ua=1&i10c.dv=14). You can find that ore underground, from my experience, you actually end up having too much of it when mining normally.

The easiest way to find it is [mining in the layers 13-16](https://minecraft.gamepedia.com/Lapis_Lazuli_Ore#Natural_generation).