OpenNetGuru

Ubuntu Linux comes with various ftp servers to setup FTP service such as:
=> proftpd - Versatile, virtual-hosting FTP daemon
=> vsftpd - The Very Secure FTP Daemon
=> ftpd - FTP server
=> wu-ftpd - powerful and widely used FTP server
=> wzdftpd - A portable, modular, small and efficient ftp server
=> pure-ftpd - Pure-FTPd FTP server
I recommend using vsftpd. It is simple and quite secure FTP server.According to vsftpd man page:
vsftpd is the Very Secure File Transfer Protocol Daemon. The server can be launched via a super-server such as inetd or xinetd. Alternatively, vsftpd can be launched in standalone mode, in which case vsftpd itself will listen on the network.
=> Default ftp port : 21
=> Default configuration file : /etc/vsftpd.conf

Step # 1: Install vsftpd
Type apt-get command to install vsftpd
$ sudo apt-get install vsftpd

Step#2: Configure /etc/vsftpd.conf

Add the following line (uncomment line) to the vsftpd configuration file:
local_enable=YES
Above config directive will allow local users to log in via ftp

If you would like to allow users to upload file, add the following to the file:
write_enable=YES

For security you may restrict local users to their home directories. Add the following to the file:
chroot_local_user=YES

Step # 3: Restart vsftpd
To restart vsftpd type the command :
$ sudo /etc/init.d/vsftpd restart

Open FTP port using iptables (optional)
Add following rules to your iptables script. Assuming that default incoming policy is drop. If protocol is TCP and destination port is 21 (ftp):
iptables -A INPUT -p tcp -m tcp --dport 21 -j ACCEPT

There are a large number of other configuration options available for vsftpd that can be used to fine tune ftp server. Read vsftpd.conf man page by typing following command:
$ man vsftpd.conf