Breaking strings is one of the most frustrating aspects of playing guitar. A broken string can bring a great gig to a grinding halt, ruin an otherwise productive practice period or slow down an expensive recording session. Strings, while not terribly expensive, can still put a strain on your wallet if you have to buy a new set every week or so. Although they may break for any number of different reasons, a few useful tips can help you prolong the life of your guitar strings.
Wipe your strings down with a clean rag after you finish playing your guitar as fingers excrete oils that can damage guitar strings. Wiping them down after each playing session removes some of these oils, thus extending the life of your strings.
Closely examine the bridge saddles of your guitar if you are having problems with only one or two particular strings breaking near the bridge. Look for any visible burrs that have formed on the saddles. Use a magnifying glass if you can't see anything with the naked eye.
File down any burrs that you find. A common nail file works well for this purpose, as does a needle file. If you accidentally put any significant scratches on the saddle, remove them with sand paper. Start with a light grit, such as 220, and slowly work your way through higher grits until the scratches are gone.
Put thicker strings on your guitar. This trick works particularly well if you have a heavy-handed picking style. While thicker strings are harder to break, be aware that they also change the feel of your instrument.
Use an electronic tuner when tuning your guitar. Using one of these tuners can help prevent breaking strings caused by accidentally over-tightening them with the tuning pegs. Just follow the on-screen tuning guide and be careful not to overshoot the proper note for each string -- E, A, D, G, B and E in standard tuning.