Bring in a tape recorder.
Teach a class, structure, or any grammar point for at least 20 minutes of classtime.
then, play the tape back and ask students what they hear. If there is a mistake, what needs to be corrected?
Students don't like to hear themselves sounding bad, and this will be a good way to help them focus on their mistakes.
It's good to do it a few days in a row...because then you can gage the results and figure out where they stand...you are just helping them in the process.