The primary spring controls the initial movement from droop to ride height (axles level)
A softer spring will make your initial travel suppler and make for a smoother ride at full droop.
A firmer spring will make your initial travel less supple and make for a firmer ride at full droop.
The Oil (30wt standard)
Using lighter shock oil reduces damping. More stable over bumps but will have the tendency to bottom out more easily.
Using heavier shock oil increases damping. Less stable over bumps but will not bottom out as easily.
The Secondary Spring (long)
The secondary spring controls the remaining 2/3 compression of the shock. It assists in resisting bottoming out.
Softening the spring will increase stability over bumps.
Hardening the spring will reduce stability over bumps.
The Pistons (B-type standard)
Using the C-type (largest hole) will reduce damping which allows the shock to rebound quicker. More stable over bumps but will have a tendency to bottom out more easily.
Using the A-type (smaller hole) will increase damping which allows the shock to rebound slower. Less susceptible to bottoming out but less stable over bumps.