Depending on the types of hard water are in your area, you may not need to make any changes. But if concentrations are above moderate (over 7 gpg or 120 mg/L or ppm), there are a few benefits you can gain from a water softener.
In the business of water softening, ion exchange water softeners offer the standard to beat. These systems have come under fire in recent years for water contamination, but they seem to be the only tried-and-true method of getting rid of hardness minerals in water. With these systems, you'll have a few extra considerations, such as what water softener salts to use and whether government restrictions will mean you have to choose from only portable exchange water softeners. Otherwise, it's all about determining the size of unit you need and looking for the most efficient model in your price range.
Relatively cheap to use with moderately hard water, chemicals are undesirable wherever drinking or prolonged skin contact may be involved. One place they do work well is in the laundry room. If the only place hard water causes frustration is in the clothes washer, adding agents such as washing soda or borax can keep the hard minerals tied up long enough to allow detergents to take care of the dirty work. There are certain benefits to each type of softening additive, and some can be harmful to the environment, so check out a few before deciding which to use.
Magnetic and electronic water softeners
Although they generally cost less, are easier to install and require little to no maintenance, there are a lot of reasons to think twice before purchasing one of these alternative water-softening devices. They come from a diverse range of brand names, and manufacturers explain performance differently, but all work on the principle that water is not chemically softened, just made to act like soft water by magnetic fields or vibrations. Some experts call electronic water softeners scams, and studies have found both positive and insignificant results of their use, so ask questions before taking the plunge and look for a product with a performance guarantee that allows return if you aren't satisfied.
This method isn't actually meant to soften water as much as it's meant to purify it, but it has the added benefit of removing most hardness minerals. A reverse osmosis filter has some big downfalls for whole-home use though; it's very costly and may involve the replacement of metal pipes due to a high potential for corrosion.