Anyone who is performing a particular job should know why they perform that job. What are the expected outcomes of that job. And they should know the correct way of performing that job in order to meet the standards in the most effective manner. This requires good amount of training. This training might have to be conducted by an expert on that particular subject. This might be on site training or a training done out from the working premises. Actually it is impossible to set particular guidelines for trainings. It is dependent on the situation. But how often you should conduct trainings. Who should generally should conduct trainings? Is lack of training the only course for the problems you face? Lean thinkers must go in to the root causes of these problems and find out the exact solutions.
Trainings are very effective when it is done in the workplace itself. It is best to have workers who are empowered to train people in day to day operations. But most importantly management must understand the requirement for the training. If it is really a requirement then they should look to train people. If it is something else which is creating that problem, then management have to look in to it and correct that cause.
Training people on the same thing over and over again is not a good practice. People will loose the interest on the trainings. People will start saying that they have not trained to get away from responsibility. Training people is good, but if and only if that is the requirement.