By Ashraf Al Shafaki
Do not correct each and every mistake of a trainee. Let some of their mistakes go 'unnoticed' otherwise this will smash down their confidence levels.
You may correct a trainee mistake indirectly by performing the action in the correct way yourself without pointing to the mistake of the trainee. He or she will learn as you perform the action correctly.
Correct only some of the trainees mistakes in a direct and clear manner. Select the mistakes that are very apparent. Ask the trainee to repeat the action in the correct way. It is not enough that he/she 'understood' the correct method, but he/she must actually perform it himself/herself more than once in order to internalize it and not for him/her to repeat the same mistake again in the future.