Effective maintenance tasks for each equipment are crucial for maintenance management. Many resources are used to design the tasks in order to improve a plant’s reliability and productivity. However, the way we incorporate all tasks in work orders (WOs) and schedule them will determine the final efficiency of our preventive maintenance strategy. 
To effectively schedule the WOs, we use different criteria to group them. Each group has pros and cons, and in practice we usually apply a combination of them to get the most of our resources and increase our department efficiency.