If you're looking for a meeting place or a good stop around ½ or halfway between San Francisco and Milpitas, you can try Redwood City, CA, which is about half an hour southeast of San Francisco, or about half an hour west of Milpitas.
Another possible place to stop near the midpoint is Foster City.
About ⅓ or a third of the way, you can stop at San Mateo, CA. This is about 17 minutes south of San Francisco.
About ⅔ or two thirds of the way, you can stop at Palo Alto, CA. This is about half an hour southeast of San Francisco, or about 17 minutes west of Milpitas.
About ¾ or three fourths of the way, you can stop at Mountain View, CA. This is about half an hour southeast of San Francisco, or about 11 minutes west of Milpitas.
If you drive straight through without stopping at all, the total distance is 46 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 50 minutes.