Iteration

Change one thing at a time and re-run your written test cases. The temptation is to rewrite the whole instruction set when something misbehaves, which usually fixes the case in front of you and breaks two you had already solved.

Keep a short changelog: what you changed, why, and what the test results were before and after. This is unglamorous and it is exactly what separates a merit from a pass — it is evidence that the improvement was real rather than a lucky run.