This is what I do and, combined with intrinsically low-acid sweat (I'm guessing), my strings seem to stay fresh longer than average. I'm aware that sometimes the other musicians I play with laugh at me for this. I don't care whatsoever as long as it works (which it does).+1 on all previous responses...wash your hands before you play the guitar (no OCD jokes, please) and wipe down the strings after every use.
Try Snake Oil Strings. They seem to last a really long time with no degradation in tone.
I don't think I'd use alcohol on rosewood. A lacquered maple neck, maybe, but no way on rosewood.I can't remember how or why I got started doing this - but I pour some rubbing alcohol on my guitar cleaning rag and rub down the strings. If you hold the rag between your thumb and first finger and run it up and down each string individually you can see how much black gunk it takes off. I'm not sure if it extends the life but it does seem to get the crud off. I also use alcohol to clean the neck, fretboard and frets when I change strings.
I don't think I'd use alcohol on rosewood. A lacquered maple neck, maybe, but no way on rosewood.
As for string life, I just play them until they're dead and replace them. I use Kerly Music's "Kerly Kues" and they last far longer than regular strings.
The following is guaranteed to increase string life dramaticallyWhen i play my guitars with new string i get so good tones that i'd like to change strings every 3 or 4 days but...time and money are a issue so i ask you: is there some method to extend the life of guitar strings?
+1 on Finger Ease. I've used this stuff since I was in my teens I think? I always spray the strings very lightly before I play up and down the entire length of the strings. Then if I'm playing for awhile, or enough to sweat, I'll spray Finger Ease on lightly the entire length of the strings and wipe them down with a micro fiber cloth during a play session. Then after I'm done, I spray them lightly again and wipe them down again, along with the bridge and pretty much the entire guitar before putting it away....but try using Finger Ease. Just spray it on a microfiber cloth or even an eye glass cleaner cloth and wipe down the strings. (works good on pickup covers and other metal too).