What are the steps of executing maintenance for plastic molds?

The first thing is to collect parts from the very last shot, before the mold is taken down for PM. If the parts are acceptable, that means that there is no repair required. Then you could just do your regular PM.
1. After taking the mold apart, divide the PM in sections. One part of the PM could be inspection of all the pins (guide pins, ejector pins, etc. ), also the inspection of bushings.
2- Another part could be the inspection of all the plates,to make sure there is no leak, and plates are not worn out, in need of resurface
3- Inspection of all the "O" rings.
4- Cleaning of the water lines
5- Inspection of the cavities, vents, finish, to see if they need to be polish
6 Finally lubrication, and antirust spray for storage.
This is just a general idea, you could add other steps depending on the mold geometry and requirements. I hope this helps.Bye

The mindset of the technician is the key to succeed the maintenance!