Guitar strings are subjected to many conditions that shorten their life, including overstretching the string, wear, and corrosion.  Here are a number of suggestions which you can do to increase the life of your strings and improve the tone of your guitar.

Simple Steps to Preserve the Tone of Your Strings

1. Right before playing, apply a small (maybe about the size of a dime)  drop of hand sanitizer and rub your hands together briskly. The sanitizer will not only kill whatever bacteria are hiding out in your palms but will also evaporate harmful oils which will dull strings.  I prefer this to just washing your hands as during handwashing, the water can soften calluses and fingernails — not a good result.
2. Do not over-stretch your strings during when you tune — this will shorten the life of the string’s elasticity.
3. Periodically, check the condition of the guitar bridge and bridge saddle to avoid breaking a string during the replacement process.
4. When you are replacing strings, do not crimp the string at the tuning peg.
5. When you’re through playing, wipe the strings with a soft cotton cloth ( an old T-shirt or even a diaper) or a microfiber cloth.  Wipe the entire strings, not just the top — wrap your cloth around the string and go up and down the length.  You should see the hand grime on your cloth.  Or check or a product called The String Cleaner, which cleans and lubricates your strings very efficiently for under fifteen bucks.
6. Other commercially available string cleaners are:  Ernie Ball’s Wonder Wipes, Fast Fret, Dr. Stringfellow, and Dunlop Ultraglide, to name a few of the most popular.  Check your local music store or browse online.

How Often Should Your Strings Be Replaced?

Of course the answer to that depends on a lot of factors including:

• What tone are you looking for (bright or more muted)?
• How often do you play or practice?  and for how long?
• What kind of string care do you perform?

If you care for your strings (and your hands before playing), here’s a guide to string life:

(courtesy of Access Rock)

And, of course, they should be replaced any time they won’t stay in tune, or you don’t like how they sound.  It’s often just a personal choice.  Good luck !