A: Leading experts suggest four guideposts: (1) We see a sustained 14 day decrease in cases; (2) Our health care system can handle the existing load; (3) We can test at least everyone who has symptoms; (4) We can trace confirmed cases and their close contacts.
Different geographies will reach these milestones at different times. Relaxing restrictions will most likely happen in a targeted, graduated manner.
Aaron Caroll’s great explainer here.