Taking Care of the Strings
The strings under greatest tension usually wear or break more quickly. Replace gut strings every few months and metal strings once or twice a year, if you use your instrument daily. Both player and instrument will greatly benefit from replacing all four strings together. The money spent is well worth it as the instrument will sound much richer. Overtones and intervals across the strings are also more accurate.
Olive oil should be rubbed into plain and metal wound gut strings when first fitted, to keep them fresh and to resist acids from the fingers penetrating the strings. It is not good practice to have a mix of different brands and/or types of strings on one instrument. A matched set of strings sound better and have a more even string tension, as well as better overtones and intervals across the strings.