From Production to development mode

So I've got a great web page developed, and now I want to make it visible to the internet. Before I do this, what are some quick modifications I have to make in the code to prepare it for production mode. For example, I know I have to set the session key value to a string, and edit the environment yaml file to have utf-8 capabilities. Anything else?

No, I meant like, a few security wary tweaks or something. For example, by setting session key, for some reason makes session stop working in development mode, but in production mode, is heavily required for security and no confusion..