Writing an application prototype - best practices?

Question

For a project I am working I want to implement a small prototype to try things out, demonstrate some functionality to the client and learn some frameworks used in the project.

Do you have any suggestions or do you know of best practices for implementing such a prototype?

Some more details:

• The application will be a complex web app
• I have to implement a mechanism where the server pushes data to subscribed clients (the data will be generated by some events)
• I want to write a prototype which implements exactly this behaviour but nothing more