Pretty much just score and salt the skin generously leave it for a while like 30 mins, soak up all the water and try to get all the salt off. Salt it a little more, rub over some oil and roast at like max temp of oven or 250 degrees for 30 or so mins. It isn't perfect crackling but it's better than chewy crackling.
Only roasts I like are chicken and lamb. I think it's because they aren't so dry.