Use your imagination to practice speaking on your own. Always find ways to vocalize the things that you're learning. Preparing for a Cambridge exam, you can find past papers with speaking part preparation and practice. Watch videos of people talking, people taking the speaking part on YouTube. Practice answering common questions about yourself. Practice speaking on a topic for a minute or two. Practice discussing your opinion on the issues of the day. Those are all specific speaking skills that you can practice onyour own.