ssh security tip allow ssh login to only certain users

As Telnet was the most common way to access a Linux server years ago, now a days it is ssh, it is secure, it is encrypted, but anyway you can improve the security even more, and today we'll see one tip to do this.
If you have a server with a lot of users that have access to it, maybe, by the console, or using a terminal, but only some of them really need to access the server via ssh. Well a good idea is to allow ssh login only to those specific users.