If your strings are looking a little dull or tarnished but are not ready to be replaced, you can clean them with a little rubbing alcohol.
It is easy, but be careful! Alcohol can be damaging to your instrument. The alcohol should not come in contact with any other part of your instrument except for the strings.
The best method is to hold the instrument upside down with the strings facing the floor, so any drops of alcohol will fall away from the instrument. Rub a small cloth with some rubbing alcohol on it over the strings a few times. Or purchase some pre-moistened alcohol pads--the kind doctors use before giving an injection. You might need to rub hard if the rosin has hardened around the strings, but it shouldn’t take too long before your strings look brand new again.