Kettle: Those bluish green flecks you sometimes see inside? They’re mineral deposits that can build up, especially if you have hard water—harmless, but not so nice to look at. To remove them, fill the kettle with equal parts white vinegar and water, bring to a boil, and let stand overnight. Rinse, then heat plain water to get rid of the traces of vinegar.
Knives: Good ones (you know, the kind you bother putting in the knife block) should never go in the dishwasher, because harsh detergents can pit the blades and high heat can damage the handles. Instead, hand wash with hot, soapy water and towel-dry. Never soak knives; this can cause handles to shrink and blades to rust. To remove stains on blades, dip a clean wine cork in mild dishwashing liquid and rub. For rust marks, use Bar Keepers Friend ($5, williams-sonoma.com). Another all-natural (if slightly aggressive) alternative: Stab a large onion a few times; the onion’s acid will remove the rust.