I would add "don't repeat yourself" as another not-so-good rule of thumb. In one of my past projects one of the most serious problems we faced was too much generalisation on early phase of development when requirements at this time were quite straight forward, but when we meet with real need of using "advantages" of our generalisation and avoidance of repeating things... well, it didn't work smoothly and even maintanance of over-engineered libraries were harder.
Of course of I am not saying that we should copy-paste everything, but adding a lot of layers of abstractions also doesn't seem neat.
Of course of I am not saying that we should copy-paste everything, but adding a lot of layers of abstractions also doesn't seem neat.