This is a classic, quick activity which can help your students focus on their cohesion when they speak, to reduce repetition and to think about the range of language they utilise when they are speaking.
Divide class into pairs, ask one students to talk about a particular subject or answer a question for one minute without hesitating, repeating any language, excessively saying “errrrr” (you can define what you consider to be acceptable depending on the level of the group) or reverting to L1. The active partner should make a note or tally of the number of times this happens and the words/phrases that the speaker repeats. As this exercise concentrates on fluency it is important that the Listener does not say anything as this could distract the speaker and interrupt their flow of speech. Swap partners, repeat and feedback.
Learning lessons from TEFL 