I think all the relevant preparation resources are listed in the mentioned PDF (except the Study Guide - which is coming soon), including the Esri instructor-led training.
Not to mention the experience you have working with ArcGIS Desktop (ArcMap/Pro) would be most essential.
Esri Technical Certification Exam
Esri will be releasing a 10.5 version of "Esri ArcGIS Desktop Associate Certification Study Guide" in late March which should be available for pre-order soon.
Do you have anything else in mind?
Think Location