How to control rendering order

I’m trying to optimize my 2D mobile game and found this section in Unity’s manual (Mobile Developer Checklist > Optimizations):

Rendering order is critical. In
general case:

  • fully opaque objects roughly front-to-back.
  • alpha tested objects roughly front-to-back.
  • skybox.
  • alpha blended objects (back to front if needed).

I totally understand why this would make a difference. But how do I do this? Multiple cameras with layers? Through code? Shaders? What’s the approach? For me, it’s all about optimization.

Render order is controlled by the render queue of the shader assigned to a material: