Blocked kitchen sink — how do I clear it without calling a plumber?

Kitchen blockages are nearly always grease + food collecting in the trap. Work up in this order:

1. Hot water. A kettle of near-boiling water down the drain softens grease. (Pour in stages — don't blast a full kettle straight onto plastic fittings.)
2. Plunger. Cover the overflow, half-fill the sink, and plunge firmly. Mechanical pressure shifts a lot.
3. Clean the U-bend (trap). Put a bucket underneath, unscrew the curved pipe under the sink, and clear the gunk out by hand. This is where the blockage usually is, and it's the step that actually fixes it.

Avoid leaning on chemical drain cleaners repeatedly — they're harsh on pipes and seals and often don't touch a solid grease plug. To prevent repeats: a sink strainer, and never pour cooking grease down the drain. If it's blocked *past* the trap and none of this works, then it's plumber time.