Here’s some great advice on pull requests from GitHub. Some of my favorite parts:

Ask, don’t tell. (“What do you think about trying…?” rather than “Don’t do…”)

Questions are so much less confrontational. This stuff might sound foo-foo but when you put it into practice and experience it for yourself, it makes a huge difference. A teaspoon of sugar makes the medicine go down.

Also this:

Try to respond to every comment.

This is a real pet peeve of mine. Ignoring comments is easily perceived as hostile behavior.