Assuming you are referring to a pull-out or pull-down kitchen faucet:
1. Unscrew the aerator from the faucet head and clean it with vinegar or soapy water. Rinse and reattach.
2. If the faucet has a detachable hose, remove it and clean with vinegar or soapy water. Rinse and reattach.
3. Use a soft cloth or sponge to wipe down the faucet body, being careful not to get any water inside the faucet itself.
4. Use a toothbrush or other small brush to clean around the base of the faucet, where it meets the sink.
5. Finally, use a clean cloth to dry the faucet completely.