What I recommend is that you start by visiting (and following!) the CCDE webpage on CLN: CCDE Design Expert.
Preparation resources for the CCDE written exam:
Go to Study Material, download the CCDE Learning Matrix spreadsheet, self-evaluate yourself against each blueprint topic, and watch the corresponding video. Then choose the resources based on the areas you need to improve on, and track your progress as you go.
Preparation resources for the CCDE practical exam:
Go to Study Material and check the preparation resources listed there, such as the Unleashing CCDE blog articles, videos, webinars, books, etc. Also, practice with the CCDE Practical demo at CCDE Practical Exam Demo - this has an old look&feel, but it’s meant for you to get the idea.
Whenever new materials are available I share the update on Twitter @elopes01 and LinkedIn Elaine Lopes, in case you want to be always in the loop.
Wish you best of luck with your CCDE preparation!!