Here's a note to ban root login, which is the first thing you do after renting a VPS.

Log in to the server as root and enter your password.

$ ssh -l root xxx.xxx.xxx.xxx

Add a user, named onojun.

$ adduser onojun

Set the password, depending on the OS, it should be set when you use adduser.

$ passwd onojun

Log out once.

$ exit

Check if you can log in with the onojun you created, you can use SSH login command as you like.

$ ssh onojun@xxx.xxx.xxx.xxx

Once you are logged in, switch to root.

$ su -

Edit the ssh configuration file. I'll make a backup for you too.

$ cd /etc/ssh
$ cp sshd_config sshd_config.old

Edit the configuration file in vim and set it to PermitRootLogin no.

$ vim sshd_config

It's at about line 40.

PermitRootLogin no

Restarting sssh

$ service sshd restart

If I can't log in as root, I'm done!