I've been reading through the style guides offered by larger tech companies. These summaries are a great place to start.
- Google developer documentation style guide Highlights
- Microsoft Top 10 tips for Microsoft style and voice
- Splunk A word about Splunk docs
- OpenStack General writing guidelines
- IBM Developer Experience Guide: Voice
- Red Hat Style guide for product documentation
- Gitlab Style guide
My takeaway: concise, conversational, active voice, you can use second person, and Oxford commas FTW.