Use tools that make it harder. Immutable datastructures, side effects constrained to a few places, good static typing etc. Those are good things, but they only

Use tools that make it harder. Immutable datastructures, side effects constrained to a few places, good static typing etc. Those are good things, but they only eliminate the class of bugs where the code is wrong. Some bugs, and most important bugs, are problems where you've written entirely valid and working code that does the wrong thing. That is where going back and reading your code again, and having layers of review from your peers, will help most.