[0xFFFE]

10. Rotate all the passwords immediately since the other guy has left the organization and have a password policy in place.

11. Understand the reason the other guy was fired make sure you are not the one holding the bag.

12. Have a issue tracking system in place, you will thank yourself later.

13. Have a change management policy in place.

14. Before you make any change full understand the consequences and have a tested plan to get back to a known good state.

[DnDGrognard]

I would add 15 start keeping a physical log book to document changes.

Dependant on what you have to look after you might want more than one book.