Not everyone likes changing guitar strings, but it’s well worth doing—and doing regularly—if you want consistently good performance. Strings on both acoustic and electric guitars go through regular wear and tear, although some wear off faster than others depending on how much they’re used. The problem most musicians have is knowing when it’s time to change strings; often, the change in sound quality and playability is so gradual that you don’t hear it yourself.
First, what makes guitar strings lose quality? Much of the damage comes from your own hands. When you play, you transfer dirt, oil, and sweat from your hands onto the strings, whether or not you use a pick. Strings will then start sounding dull or out of tune. At first, you may notice that you need more force to get the right sound or volume out of them. Most players will take this to mean the guitar needs tuning, but you know it’s time to change the strings when you need to retune more often than usual.
Another factor in string wear-out is humidity. This is especially true with metal strings, which corrode when exposed to wet or humid conditions for too long. Avoid playing with sweaty hands, or wipe your hands on a clean towel before playing. Of course, this would be unavoidable during long performances. Your best bet in this case is to take breaks as often as you can, and try to play with lighter hands—heavy-handed playing can strengthen the damaging effects of humid air.
Most guitar strings, when played regularly, will last a few months before the quality gets drastically altered. If you’re not sensitive to changes in sound quality, try feeling for changes in texture. Dirty strings tend to feel more slippery than usual as oil builds up on the surface. You can also run a white rag or piece of paper over the strings; if it comes out a little discoloured, then there’s probably enough dirt to merit a new set of strings.
Sometimes you’ll even want to change the strings on a brand-new guitar. It’s safe to assume that an instrument gets tested by dozens of people every day—that’s dozens of dirty hands handling your guitar even before you start playing it. This tends to happen in large music shops. You can buy a new set of strings on the spot and have them put them in while you wait; at a decent shop you might even get this service for free.