Check your local bike shops. There's probably at least one that hosts group rides and may offer clinics and tutoring. A well organized group ride is a great way to get accustomed to riding on streets. Some well organized group rides include traffic control by law enforcement and volunteers, which can minimize contact with routine vehicle traffic. Even a non-officiated small group ride can help build confidence, as vehicle drivers tend to recognize and give courtesy toward groups that are obviously riding with experience and confidence (as opposed to a clot of schoolkids riding toward traffic and weaving around wildly).