Fine tuning a heli is a series of steps taken to eliminate as much vibration as you can and tweaking needle tuning, pitch and throttle curves.

Start by working on the blades, make sure they are balanced both for weight and that the cg's are matched. Try to get the tracking perfect. Measure the fly bar to make sure the paddles are as close to perfectly equi-distant from the head, make sure they are perfectly level with each other and level to the head.

Sizing ball links, eliminiating any drag on the tail rotor linkage, I could go on and on.

Its kind of like rough shaping a piece of balsa with 80 grit and working your way closer to perfect with finer and finer grits till its silky smooth.