Make sure the skin is as dry as it can be. Take it out of the fridge and let it air for as long as possible. Dry it with a tea towel. Moisture is the enemy.

Score skin with a sharp knife. Rub lots of salt and veg oil into skin. Don't use olive oil. Some people swear by adding lemon juice to the mix but I never have.

Have oven up very, very high to start (first 20-30 mins) the turn down to just high for remainder. Google cooking times dependent on weight. I always forget!