My advice:
Pay particular attention to section to section 2.1 of the VCDX5-DCV Design Defense Blueprint.
The goal of the application is to represent your skills as a VMware Solution Architect to a group of your peers who do not know you or your work. If you can convince them that you understood the customer's needs, considered how those needs could be best served by the tools at your disposal, and designed a solution that met those needs - you will be successful. How you arrived at your design, what influenced your decisions, and how you managed the risks inherent in your decisions are extremely important.
Also extremely important is how well you prepared your customer to deploy the solution you designed. Implementation documentation is time-consuming and often jobbed out to specialists. However, it is a skill you must demonstrate mastery of if you are to become VCDX.
Mark Brunstad
VCDX Program Manager