New mandolin strings are typically dry. It helps to wipe the strings regularly with a bit of oil so that it is easier to slide up or down the strings when playing. A music store will carry oil for strings, but even a very light coat of furniture polish will work. You can use a soft cloth to apply the oil easily.
The mandolin strings should be maintained so they are up to tension when you are regularly playing the instrument. The mandolin is a rather fragile stringed instrument so you want to make sure that it is not tuned higher than what is appropriate or you can harm your instrument. Tuning is the same as that of a violin, or in the GDAE range.
Clean your strings every time you play your mandolin to get rid of the grime and oil that accumulates from your fingers. Always use a clean, soft cotton cloth.
Replace your strings on your mandolin regularly to ensure the best of sound.
If you are not using the instrument on a routine basis, then the tension should be brought down about three half tones.