Keeping changes small

A small change is easier to review and easier to undo. These are the checks I run before I call one done.

Write less

Write the least code that solves the problem, and nothing speculative.
Skip options, flags and settings nobody asked for.
Don't build an abstraction for code that's used once. Three similar lines are easier to read than the helper that replaces them.
Validate where data comes in from outside, like user input and other people's APIs. Inside your own code, don't handle errors that can't happen.
If 200 lines could be 50, rewrite it.
If there's a simpler way than the one you were asked for, say so before building the one you were asked for.
Ask whether a senior engineer would call it overcomplicated. If the answer is yes, simplify first.

Every changed line should trace back to the request.
Match the style around you, except for the rules you've decided always apply. Mine are in How I write React.
Leave nearby code, comments and formatting alone. Tidying them on the way past makes the diff harder to review.
If you spot dead code that isn't yours, mention it and leave it. Remove only the leftovers your own change created.

Do a simplify pass over the final diff. Whoever wrote it, and coding agents especially, tends to over-deliver: an extra helper, an extra parameter, a comment on every hunk. That's cheaper to strip before review than after merge.
Run the checks again afterwards, since cutting code can break it.