When creating a XEN keep it focused. Describe together only the enhancements which should be introduced together. Otherwise, it is better to split it into several more focused documents.
To avoid clashes, when opening a PR with the new XEN assign it number 999. The final unique number will be assigned as a part of the review.
When suggesting a new node, always provide a full description for the node and its pins so that anyone can better imagine the behavior. Finally, its author can merely copy-paste documentation from the XEN.
Think about UX in general. Many times the feature requests are a technology creep or too academic. What does the enhancement mean for the most of xoders? How does it improve their experience? At the very minimum doesn't it make things worse for typical scenarios? Include a section about UX if applicable.
Think about backward compatibility. Was everything designed in a way that existing projects, articles, and videos will keep working after the improvement is implemented? Include a section if applicable.