3. Grease, oil and butter: draw it out before any water touches it
Oil stains are the ones people most often make worse, because the instinct is to wet them. Water and oil do not mix, so water just spreads the oil into a wider, fainter ring while sealing the original centre.
Start dry. Scrape off any solid residue with a blunt knife edge. Then cover the mark generously with an absorbent powder — cornflour, talc or bicarbonate of soda all work. Leave it at least thirty minutes, and for a heavy stain on a suit or a tablecloth, leave it overnight. The powder wicks the free oil up out of the weave. Brush it off outside or straight into a bin.
Next, a surfactant. Work a few drops of ordinary washing-up liquid into the remaining mark with a fingertip or a soft toothbrush, in small circles from the outside inward. Dish soap is formulated specifically to lift fat, which is why it outperforms most dedicated stain sprays here. Leave it for ten minutes.
Then wash as hot as the care label allows. This is the one family where heat helps — it keeps the fat liquid so the detergent can carry it away. Cold washes are the usual reason a grease stain reappears as a dull shadow after drying.
Check before drying, because once a garment goes through a hot dryer with oil still in it, the stain oxidises and turns yellow-brown permanently. Old set-in oil marks sometimes respond to a solvent-based spot remover, but the success rate drops sharply after the first wash.