Start unified sniffing and select your interface
scan for hosts

Under plugins - use the plugin to isolate the IP of the gateway

in the host tab, assign the gateway ip to target 1

leaving target 2 blank will auto assign all ALREADY scanned hosts to be poisoned (not recommended for wifi - cards simply aren't fast enough to deal with more than a few hosts at a time) - or assign specific hosts for poisoning

select the arp poisoning attack and enable sniffing of remote connections

go to plugins and then activate the auto add host plugin by double clicking

hope this helps.