The Restaurant Law Center of National Restaurant Association (NRA) updated its guidelines on September 10, 2020. These now establish parameters for food service establishments as they reopen. We find the National Restaurant Association table spacing rules far-reaching, and therefore append a link to the complete document below. However, we should mention details may vary between states and cities, as is the case with the images from City of Portsmouth where they add space for seating.
National Restaurant Association Table Spacing and Occupation Rules

1… Tables must be six feet apart, with no more than eight guests per table.
2… Moreover, restaurant staff must limit customer numbers in terms of these arrangements.
3… However, social distancing rules apply at restaurant entrances, exits, and bar areas.
4… Signage or floor-tape must be in position to mandate these standards.
5… Finally, only one member of each guest party may be present in waiting / pick up areas.
The National Restaurant Association Addresses Every Detail

These National Restaurant Association table spacing guidelines form part of a broader document addressing restaurant hygiene during COVID. For example:
1… Hand washing is stipulated without mentioning frequency.
2… High customer-contact areas require cleaning every two hours.
3… Drink refills should be in clean / unused glasses or cups.
3… Laminated menus require cleaning after each use.
4… However paper menus must be disposed of after a one use.
5… Single use accessories (napkins, condiment sachets) are encouraged.
6… Moreover, hand sanitizer and related products must be readily available.
7… There must also be a documented plan for disinfecting contact surfaces.
8… However, one dedicated staff member on each shift shall sanitize those surfaces.

This comprehensive document also has other sections addressing employee safety and hygiene, and measures for controlling spread. As well as customer health checks and sanitizing tables and chairs between customers. We provide this information because we believe all concerned should understand the official position. Then we can work together safely to reopen our societies again.
Related
Guidance for Retail Employers and Workers
Is Three or Six Feet Social Distancing Safer
Preview Image: Bar to Table Spacing