First we must edit the SSH daemon config file. Though under different Linux distributions this may be located in different directories, usually it is stored under /etc/ssh/sshd_config
Use your text editor to change the values set in this file, all lines starting with # are commented out and must have this character removed to take any effect. A list of recommendations follow as such.
Port (chose a number between 0 - 65535, normaly greater than four digits)
PasswordAuthentication yes
AllowUsers user1 user2 ...etc
Note that it is preferable to disable password logins all together and use SSH Keys for improved security as explained in this document.