The easiest way to learn all the best bicycle routes in your area (as well as learn how to take care of your bicycle and to ride safely) is to join a local bicycle club. The 2 most beginner-friendly Silicon Valley bicycle clubs are Western Wheelers (
Western Wheelers Bicycle Club - Home Page) and ACTC (
Almaden Cycle Touring Club). Both let guests (non-members) ride with them for free. Both have detailed ride schedules on their web sites that describe the length and difficulty of their scheduled rides. Both clubs offer rides that are suitable for beginners (10-20 miles with easy terrain and easy pace) as well as harder rides.