Consider making the first offer when you have a pretty good sense of where the ZOPA is in order to anchor the negotiation in your favour.
If you don’t know the ZOPA, hang back and let the other side make the first offer, or make a soft anchor, e.g. “We’re thinking about something in the ballpark of $30.”
When you don’t know the ZOPA, but your opponent does, resist their attempt to anchor you.
Default to a first offer that is more aggressive than your instincts might lead you to make.
Ask: What is the highest number that I can justify?