Buy lamb's or calf's liver for grilling, chicken liver is typically used to make pate. Liver should be cooked absolutely fresh. Buy it on the day you plan to cook it and make sure it looks clean and shiny with no dry edges or discolouration. Avoid it also if it has a green tinge to it - it is stained with bile from the gall bladder and will not taste good.
Refrigerate on a plate covered with plastic wrap - removing any wrapping from the butcher. Use within 24 hours of buying.
Tips & Tricks:
Before cooking make sure the liver is free of its protective membrane. Otherwise it will shrink and make the the liver curl.
To grill, slice liver 1 cm thick and lightly oil each side with olive oil. Cook for 3 minutes each side under a pre-heated grill.