How do you adjust a Shimano rear derailleur for optimal performance?

To adjust a Shimano rear derailleur for optimal performance, start by ensuring the derailleur hanger is straight. Then, shift to the smallest cog and adjust the high limit screw so the upper jockey wheel aligns with the smallest cog. Next, shift to the largest cog and adjust the low limit screw so the lower jockey wheel aligns with the largest cog. Finally, fine-tune the indexing by adjusting the barrel adjuster until the shifting is smooth and precise.