Playing
Frequently playing the guitar to adjust the strings is the most obvious and effective way to break them in. However, this method can take a few days or a week before the strings are well-adjusted to your guitar and less susceptible to becoming out of tune. A simple song played with the rest of the strings on your guitar is a starting point. Each time you lose the correct tone on the string, retune it and then keep playing.
Bending
Some tricks that test the strength of the string will help you break it in faster. Bending requires you to push the string up with your finger, or pull it down. This method could make the string go out of tune faster, but the motions of putting it out of tune and then retuning will help you break it in. The whammy bar, which is situated at the body of many electric guitars, can also help you break the string in by bending it.
Pressure
Playing the guitar puts the majority of strain on the strings from the body to the nut, but the string from the tuning peg to the nut also needs strain. After winding the new string around the tuning peg, a push on the string between the peg and nut will tighten up the tension on the wrapped part of the string on the peg. Tuning the guitar after pushing down on the space will help ensure your string doesn't go out of tune as fast.
Types of Strings
Guitar strings are broken into three categories, including electric, acoustic and classical. The electric stings are usually nickel-plated steel, which is then wound around carbon steel or stainless steel. The strings also contain some iron, a magnetic metal that can be detected by the guitar's pickup. Acoustic guitars are usually made of bronze or phosphor bronze. However, the center of the string is steel. Classical guitars use nylon strings which also usually include bronze or silver.