B. J. Fregly's tips on writing for the Journal of Biomechanical Engineering.
I find passive voice indirect. I avoid passive voice when appropriate, but not always. In this context, I love the following comparison: "why did the chicken cross the road?" versus "why was the road crossed by the chicken?"
Here's a beautiful essay on how to write an article containing mathematics. The intended audience of this essay was MIT undergrads, but the lessons are broadly applicable. The part about language on pages 3-8 is especially compelling.
Good programming style. Here's one on MATLAB programming style guidelines, in which the author quotes regarding variable naming, "A rose by any other name confuses the issue."
The PLOS family of journals had series of essays called "Ten Simple Rules," covering various topics of general interest: ten simple rules for getting published, for getting grants, for reviewers, for selecting a postdoctoral position, for a successful collaboration, for making oral presentations, for a good poster presentation, for doing your best research, for graduate students, organizing a scientific meeting, etc.