Tell the guide how your group uses English and how much detail you want. Historical context, architecture and contemporary life call for different explanations. This is more helpful than simply requesting an English-speaking guide.
Keep a destination list in Chinese and English, retaining the Chinese names for maps, reservations and meeting points. Agree whether you prefer conversation while walking or explanations at each stop.
Confirm tickets, transport, meals and fees in writing where possible. Language availability and the scope of the service are separate matters to clarify.