They always designed first before they got to writing code. I am talking three weeks of design and not a single line of code. In fact, the coding just takes two or three days for any feature for them. The amount of emphasis they gave to design taught me how important design is.
They made extremely good code review comments (which actually made the entire engineering team better) and always had the time for it. I haven't seen anybody take such good care of their code.
The third one is more of a non-technical thing. Something that they taught me, whenever you come up with a solution, think of ways to break it, for the first solution you come up with is more often than not the worst solution you could come up with.