Say a sentence at natural speed and ask learners to write down what you said. You'll probably need to repeat several times. Don't slow down your speed unless it's absolutely necessary. Then ask a learner to read the sentence to check it. Finally, write it for all to see (or ask an advanced student to write it) and then say it again a few times at natural speed. For a twist, ask a learner to dictate a sentence for the rest of the group. Learners will be thrilled if their teacher (you) can correctly understand what they said.