Wash it down under the cold tap to remove any sand.
Slit the ventral side open and pull out the guts. Discard immediately and rinse out the cavity.
Starting from the head cut along the dorsal side as deep as the spine to the caudal fin.
Ignore advice to run the knife along the bone as this wastes a lot of fish and you end up with a fillet full of bones.
Instead cut downwards pressing against the bones.
Keep moving along until the fillet is freed.
You should have a good view of the skeleton now. Slide the knife under and work it along to remove the skeleton, discard.
Turn the fillets skin side up.
Scrape off the scales using a knife .