Several years back in a talk about rapid prototyping with Smalltalk, of all things, Kent Beck gave out some advice on technical writing that stayed with me. He recommended targeting a single type of audience, rather than trying to speak to several. He argued that if you are writing consistently for one type of audience, others audiences can adjust, but if you skip between target audiences, you risk making everyone seasick.

To help keep yourself on target, Beck recommended that before you start to write, you first write out a short description of an ideal member of your target audience. Who are they? What do they do? What problems do they have? How will reading what you're about to write help them? Then keep this description in front of you (or within quick reach) while writing, and refer to it whenever you're in doubt about how to address a topic.