Highly charged ions interact strongly with water, breaking hydrogen bonds and inducing electrostatic structuring of nearby water, and are thus called "structure-makers" or "kosmotropes". Conversely, weak ions can disrupt the structure of water, and are thus called "structure-breakers" or       
"chaotropes". The order of the tendency of ions to make or break water structure is the basis of the Hofmeister series.
Hofmeister discovered a series of salts that have consistent effects on the solubility of proteins and (it was discovered later) on the stability of their secondary and tertiary structure.  Anions appear to have a larger effect than cations, and are usually ordered
(kosmotropic)   : (chaotropic)
(This is a partial listing; many more salts have been studied.)
The order of cations is usually given as
(chaotropic)   : (kosmotropic)
When oppositely charged kosmotropic cations and anions are in solution together, they are attracted to each other, rather than to water, and the same can be said for chaotropic cations and anions. Thus, the preferential associations of oppositely charged ions can be ordered as:
kosmotrope-kosmotrope > kosmotrope-water > water-water > chaotrope-water > chaotrope-chaotrope
Combining kosmotropic anions with kosmotropic cations reduces the kosmotropic effect of these ions because they are pairing to each other too strongly to be structuring water. Kosmotropic anions do not readily pair with chaotropic cations.  The combination of kosmotropic anions with chaotropic cations is the best ion combination to stabilize proteins.