Clarity, both on my understanding of the problem and in my understanding of my tools. Simplicity and readability of my code, my tests, and the notes that accom

Clarity, both on my understanding of the problem and in my understanding of my tools. Simplicity and readability of my code, my tests, and the notes that accompany my code. That way someone (including my future self) can understand the system. And writing tests first. I've become convinced that there are very very few cases when I can afford the luxury of not insisting on writing a test first.