Motivate others? Provide a good role-model yourself. Show others what can be achieved not by trying to impress with your skills but by leading others into an activity and praising every part of their effort that is effective.
If you are faced with people who just do not want to carry out the tasks in front of them, you have to ask if the task is necessary, appropriate or could be altered. Generally speaking, there is nothing more motivating than the personal experience of success. Can you arrange to make this happen, even if in small steps?