5. Avoid programming cleverness. Instead, assume a good compiler and write readable code.
Cycle-counting and compiler-specific optimizations are favorite pastimes of hackers, and sometimes they're important. But we could never have completed the Graphing Calculator in under six months had we worried about optimizing each routine. Rather, we dealt with speed problems only when they were perceptible to users.
We made no attempt to look at performance bottlenecks or at the compiled code of the Calculator until after running execution profiles. We were surprised where the time was being spent. Most of the time that the Calculator is compute-bound it's either in the math libraries or in QuickDraw. So little time is spent in our code that even compiling it unoptimized didn't slow it down perceptibly. Improving our code's performance meant calling the math libraries less often.
Programmers are often tempted to spend time saving a few bytes or cycles or to fine-tune an algorithm. If the change isn't visible to users, however, the benefits may not extend beyond the programmer's satisfaction. When most of the code in an application is straightforward and readable, maintenance and improvements are easier to make. Those are changes that users will notice.