Find a Mandarin speaker who is learning English on Tandem, chat by text for a day or two, then suggest a call: a time, and how you will split it between the two languages. Write the suggestion in Mandarin with the Pinyin keyboard built into your phone (iOS and Android both ship one), or in pinyin. On the call, keep a notebook open and write down every word your partner has to explain.

Your partner is a learner too, so mistakes are expected on both sides. Ten minutes of real conversation teaches more than an hour of worrying about it.