Never
me too, i never change the strings, instead i´m buying a new guitar instead, works so much better and gives you immediatly the BOOOM
lol
just joking.
i change the strings on my two main axes quite often during regular time (if i´m not recording anything), about a new set all 2 weeks
i´m using ernie balls and pyramid on them.
i play my main guitars every day for at least one hour
but on the other guitars i have, on some i have elixier and on some ernie balls or pyramid too, and i change those about all 2 months, and the ones with elixier about all 3 months
and of course i clean the strings with a cloth after playing
its not about dirt or crust on the strings, if you have already rust on your strings its really about time to change the strings as the rust can also damage your frets and you have more fretwear on them.
but you notice that the strings get old when they go often out of tune and the intonation isnt good anymore too, and this is what me annoys the most on old strings.
i buy all my strings in big bulk familiy packages to save some money, doesnt make sense either to invest lots of money in good guitars and then you cheap with guitar strings and never change them