Basic Rules

Plan
Maintenance should start with proper planning. A risk assessment should be carried out and workers should be involved in this process.
Make it safe
The work area needs to be secured by preventing unauthorised access and needs to be kept clean and safe. Warning cards should be attached to machinery,
Use the appropriate equipment
Workers involved in maintenance tasks should have the appropriate tools and equipment, including appropriate personal protective equipment.
Work as planned
Safe work procedures have to be communicated, understood by workers and applied correctly, even when there is time pressure.
Final control
The maintenance process needs to end with checks to make sure that the task has been completed and that the item under maintenance is in a safe condition.

More information on the section dedicated to maintenance on the EU-OSHA website.