Error Correction
There are many ways to correct mistakes when using role-play. It is rarely appropriate for the teacher to jump in and correct every mistake. This could be incredibly demotivating! Some students do like to be corrected straight after a role-play activity, while the language is still fresh in their minds. Sentences with errors can be written on the board for the group to correct together.
Self-correction - If you have the equipment to record the role-plays either on audiocassette or on video, students can be given the opportunity to listen to the dialogue again and reflect on the language used. They may find it easy to spot their own mistakes.
Peer-correction - Fellow students may be able to correct some mistakes made by their peers. Students could be asked to listen out for both great bits of language they'd like to use themselves, and some mistakes they hear. Be careful to keep peer-correction a positive and profitable experience for all involved.
Making a note of common mistakes yourself and dealing with them in future classes ensures that the students don't lose motivation by being corrected on the spot or straight after the role-play. Negotiate with students and ask them how they would like to be corrected.