Install dsniff o any package that furnishes arpspoof
Enable IP forwarding with echo 1 > /proc/sys/net/ipv4/ip_forward
Start the Arp spoofing with arpspoof -i eth0 -t 192.168.0.3 192.168.0.1 where -t is the target ip and the following is the ip of the gateway. This way the target computer will think our computer is the gateway and will route all packets through it. The local pc will then forward all the packets to the real gateway
Use Wireshark on the local network interface (eth0, in the above case) to sniff the traffic