Components of a Great Architecture Diagram

Info - key, author, legend, version history
Flow diagrams
VPC and markings
Services wrapped up
Understand the different scopes - overarching be more general "image service" but a more indepth diagram would include the components or even the classes of that service etc.
Organise it from right to left or top to bottom
Try to avoid the mess of arrows
Use the C4 Model
Mark clear domain and service boundaries
Add interaction comments
Record questions asked about the diagram, along with the diagram
Record an explanation of the diagram
Have both short term and long term vision for the architecture