Whether you are cooking whole, butterflying or using the fillets, rubbing sardines with olive oil, salt and pepper before cooking makes for a deliciously unctuous fish. Another good general tip is to dress cooked sardines in lemon juice after cooking as Shaun Hill advises, this counters the intense oily flavour of the fish.
Part of sardines' charm is that can be cooked quickly and easily, hence why they are often for breakfast. You can tell they are cooked when their flesh is firm, opaque and easily flakes away from the bone.
When the weather is nice, whole sardines are perfect fish for the barbecue. They cook very quickly on a hot grill (3 - 4 minutes on each side) so make a beautifully quick and simple al fresco starter. You could also roast sardines whole in the oven and serve with a sauce.
Sardines can be descaled, gutted and grilled simply, as in Nathan Outlaw’s recipe. Sardine bones are so small that you can eat them without too much worry.
Sardine fillets can be grilled or pan-fried. Shaun Rankin and Adam Gray’s recipes both use grilling to great effect, first rubbing the fillets with olive oil, a knob of softened butter and a squeeze of lemon juice before grilling skin-side up until the flesh is cooked through and the skin is golden and crispy.
Perhaps one of the simplest ways to cook sardine fillets is to pan-fry them - the fillets cook very quickly, and cooking skin-side down in a hot pan again allows for wonderfully crispy skin.