My approach to tech writing (of which I have done a lot) is to pick an existing style you like and follow that. For example, when I was writing the docs for the API for a multi-site library we were providing I did it in the Win32 help-file format that MS used. This was a good format, and we were MSs auditors at the time so no-one could complain. I did it with a bunch of Word styles.

But of course content is far more important than format. IMHO, if you are not a good English writer, you are probably not a good dev.