its easy buddy just fillet the fish(trevally,yellowtail,bonito,tuna, slimys)
use a piece of plywood or something underneath so you dont get juice seeping away
get an old newspaper lay on wood
add a layer of butchers salt about 5-10mm on paper
place fish skin side down on paper
add a layer of salt on top about10-20mm thick depending on thickness of fillet(more salt for thick fish)
leave alone for 2-3 days or until you remember them.lol
dust off salt and place in zip lock bags.
now the fillets will last for over a year if you dont use them before that..
good luck, its real easy..cheers stevo..