Method It provides the ways or manner in which a task is to be performed. They are standardised ways to perform routine jobs and are considered standing plan.
It may be a step of a procedure, e.g. methods of training, methods ofrecruitment, etc.
Rule It is a specific statement that informs what is to be done and what not. There is no discretion allowed in rules. They must be strictly followed and one cannot make changes in them.