Cornwall is best eaten within sight of salt water. The county's coastline is a string of small harbours where the day's catch comes over the wall in the morning and appears on a chalkboard by lunchtime. You do not need to book months ahead or chase awards to eat brilliantly here — you need to know which village does what, and when to turn up.

Eat where the boats are moored

The single most reliable rule on the Cornish coast is proximity. A pub, café or shack within a few hundred yards of a working quay has almost certainly got fresher fish than anywhere a mile inland. Working harbours such as Newlyn, Mevagissey, Porthleven, Looe and Padstow still land fish, crab and lobster daily, and the food around them reflects that.

A few things worth looking for:

• A changing menu. Handwritten boards with a date on them suggest a kitchen cooking what it bought that morning rather than a freezer schedule.
• Species you would not plan around. Pollack, gurnard, hake, John Dory, spider crab and cuttlefish all turn up in Cornish kitchens when they are running.
• Local boats named on the board. Plenty of places credit the boat or the harbour their catch came from — a good sign, and a good conversation starter.
• A queue at odd hours. If locals are collecting lunch at half eleven, join them.

The pasty: rules worth knowing

The Cornish pasty is a protected thing with a defined shape, and the version worth eating is simple: skirt steak, potato, swede and onion, seasoned, crimped along one side, and baked so the filling steams inside its own pastry. No carrot. No peas. Peas in a pasty are a confession.

Buy from a shop where they come out of the oven in waves rather than sitting under a heat lamp all afternoon. Ask when the next batch is due; most bakeries will tell you honestly. Eat it warm, out of the paper, sitting on a harbour wall facing the water. If you are walking the coast path, a pasty wrapped in greaseproof is the finest packed lunch in Britain — it travels better than a sandwich and does not mind being slightly squashed.

In fishing villages such as Mousehole, Cadgwith and Polperro, you will also find the "tiddy oggy" — a smaller, simpler version that was traditionally a miner's or fisherman's pocket meal. It is worth trying for the history alone.

Crab, lobster and the shellfish shacks

Cornish crab is sweet, pale and best treated with restraint: white meat in a sandwich with good bread and a squeeze of lemon, brown meat spread on toast with a pinch of pepper. Quayside shacks at places like Coverack, Mullion, Port Isaac and St Mawes do this beautifully between spring and early autumn.

Practical notes:

• Brown crab is available most of the year, though it is at its best in late spring and summer.
• Lobster is generally landed in greatest numbers from spring through autumn; prices rise sharply around bank holidays.
• Order dressed crab if you want the work done for you, and ask for it cold rather than warmed through — heat dulls the sweetness.
• Bring cash. Small shacks and harbour stalls often prefer it, and mobile signal in some coves is patchy at best.

If you are buying shellfish to take home, ask for it cooked and packed with ice, and eat it the same day. Shellfish is not a souvenir to leave in a warm car boot while you visit a garden.

Day-boat fish and how to spot it

The Cornish fleet is largely small and inshore, which is why the fish is so good. Look for menus built around the season rather than a permanent printed list. Mackerel is superb from late spring through autumn, and a grilled fresh one with nothing but butter and lemon is one of the great cheap meals of the south-west. Monkfish, turbot and brill appear on smarter menus; hake, whiting and gurnard are the everyday heroes.

In Newlyn, Fowey and Mevagissey you can often buy straight from a fishmonger within sight of the harbour. Ask what came in today, ask what to do with it, and be honest about your cooking ability — fishmongers are generous with advice and will happily fillet and pin-bone for you.

Cream teas and the jam-first question

A Cornish cream tea is a split scone, strawberry jam, and a generous spoon of clotted cream on top. In Devon they do it the other way round. Both are correct; only one is Cornish. Clotted cream should be thick enough to stand a spoon in, and the scone should be fresh that day — a stale scone with excellent cream is still a stale scone.

Village cafés and church hall teas in places like St Keverne, Boscastle and Marazion serve the best versions, usually from Easter until early October. Expect to pay a few pounds, and expect the tea to arrive in a proper pot.

Practical notes for a coastal food crawl

• Go out of season if you can. May, June and September offer the best combination of open kitchens, landed fish and breathing room.
• Eat early or eat late. Between midday and half past one, harbour pubs fill fast with walkers and families.
• Park outside the village and walk in. Most Cornish harbours have narrow lanes and very little parking; the walk is usually the nicest part anyway.
• Carry cash and a reusable bag. You will buy fish, cheese or a bag of saffron buns on impulse.
• Check tide times, not just opening hours. A few minutes' planning turns a good day into a great one, especially around the smaller coves.

Cornwall's coastal villages are not museums. They are working places that happen to feed visitors exceptionally well. Turn up with an appetite, ask what is good today, and let the tide set your timetable.