My advice is:

1. Add the learning plan on Nutanix University for the certification you plan to take, and take all the courses. Be sure to take the practice exam, and take note of the topics you need to practice more on.
2. Read the documentation, when you need to understand a specific topic. You may also consider reading the Nutanix Bible.
3. Take test drives! Even if you have a lab environment own, the test drives can be a very useful way to get to know Nutanix.

Best of luck!

Also I can share some my prep guides

NCA:

https://vmik.net/2020/12/21/nca515-prep-guide/

NCAP (NCM-MCI): 

https://vmik.net/2020/03/26/ncap510-prep-guide/

NCP-DS:

https://vmik.net/2021/04/22/ncp-ds-prep-guide/

They are in russian, but translate button in the left bottom corner. I hope it can help.

Make sure you review the exam blueprint guide for the exam you plan to take, that comes from the documentation the exam item writers are given and lays out the knowledge areas covered by the exam.