sudo vi /etc/network/interfaces

## To configure a dynamic IP address
auto eth0
iface eth0 inet dhcp

## Or configure a static IP
auto eth0
iface eth0 inet static
  address 192.168.1.14
  gateway 192.168.1.1
  netmask 255.255.255.0
  network 192.168.1.0
  broadcast 192.168.1.255

For these settings to take effect you need to restart your networking services.

sudo /etc/init.d/networking restart