I listened to Mark Erikson's talk about how he made Immer twice as fast. Here are some notes that stood out to me.

How to approach debugging

Understand what the problem is.
Reproduce it and understand when it's happening.
Determine why the problem is happening, then narrow down the possibilities using a hypothesis, test, and experiment approach.
Trace it to a root cause.
Find the best way to fix it — it could be changing one line, changing a component, or changing the system approach. Fix the root cause, not the symptoms, and understand the constraints, severity, and code requirements.
Document as much as possible.
Use the right tools for the job. Keep a lot of tools in your toolbox.
Be willing to dig into abstractions and look at underlying implementations. Sometimes that means looking at lower levels of code to understand behavior, and that includes third-party libraries. Be willing to dig into unfamiliar spaces in the code, including code you don't own, to understand what is happening beneath it.
Eliminate unnecessary work.
Cache work that has already been done.
Parallelize the work across threads and machines.
Set up a benchmark so you can test it now and after the implementation.

How to Approach Debugging by Mark Erikson