In his book on photography, Dick Boer gives two useful rules for focusing, which I have found invaluable when using a folder.
To get both the background and a near object sharp set the focusing to 30 feet (10m) and set the lens to f/8. You will get sharp focus from 18ft (6m) to infinity. This is effective for landscapes, street scenes and buildings.
For near subjects set the focusing to 12 ft (4m) and the aperture to f/8. You will get sharp focus from 9 ft (3m) to 20 ft. (7m). This is effective for groups and any close subject more than three paces away.
Boer continues: “Drill yourelf thoroughly in these two rule. They will help you enormously. You will take a sharp picture while others are still fumbling with their focusing. Always use f/8.”
So, that's a rule of thumb, for what I want to do, of f8, focus at 12', speed according to light. Voila!