I am aware that this could be seen as subjective but this is definitely not my intention. I am always on the hunt for techniques that I may have never heard of that help improve both productivity and quality of software engineers.
In particular I am looking for tools, techniques, approaches, tips and tricks, best practices, etc. that helped you to improve both your productivity and quality as a software engineer. This is actually a process related question. So please don't answer with your opinion about which programming language is the best from your perspective.
I expect the answers to be subjective. But that is the beauty of it. Not everything works for everybody. We all have a different set of constraints that we operate under. Therefore it is unavoidable that we make different choices. If the answers are contradictory, that would be perfectly fine!
What were the techniques that were helpful to you specifically? How did they make a difference? What criteria do you use to come to that conclusion?