The generic method of saving iptables rules is to use the command iptables-save, which writes to stdout.

iptables-save > /etc/network/iptables.rules

The output created by iptables-save can then by read on stdin by iptables-restore.

If on a server, without NetworkManager, a common approach is then to use a pre-up command in /etc/network/interfaces.

iface eth0 inet static
        ....
        pre-up iptables-restore < /etc/network/iptables.rules

NOTE: Do note that the commands iptables, iptables-save and iptables-restore are IPv4 only. For IPv6 traffic the equivalent commands are ip6tables, ip6tables-save and ip6tables-restore.