If you're looking for a meeting place or a good stop around ½ or halfway between San Francisco and Fairfield, you can try Hercules, CA, which is about half an hour northeast of San Francisco, or about half an hour southwest of Fairfield.
About ¼ or a fourth of the way, you can stop at Berkeley, CA. This is about 11 minutes northeast of San Francisco.
About ⅓ or a third of the way, you can stop at Richmond, CA. This is about 16 minutes north of San Francisco.
If you drive straight through without stopping at all, the total distance is 47 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 52 minutes.