Good product writing is conversational. So use words people would actually say to each other in a conversation. Imagine you’re talking to a neighbor or friend you admire. How would you describe this feature to them? Think out loud to them as you write, and read your work aloud to review it. Keep editing and refining the language until everything is clear, friendly, and useful.Good product writing is conversational

The entire article is a great piece but the above quote from Nicole Fenton stands out as one of the best pieces of 'great UX' that I've come across in a very long time. I've previously discussed why I think it's important for designers to write.