How to block root SSH connection and only allow user SSH connection?

I never do a lot to secure SSH, other than offset port from it's default value. Even then, I still login as root 99% of the time, which isn't good practice obviously. Granted, these are just for personal VPSes that aren't really used for much other than messing around and learning purposes.

I was wondering how I could deny root connections and only allow a custom user to have sudo access.

For example, my server has the following users: root John

I want to disable root logins, and only allow 'John' to be able to use sudo if needed for system wide changes. How would I do that?

John is not in the sudoers file. This incident will be reported.

I'm using a Debian 6 32bit Minimal OS.