Some abbreviations in common use:
A/A: answers all
A/F: answers few
A/M: answers most
A/S: answers some
DOB: date of birth
ICR: I can return
LLP: long letter pals
NPW: new pals welcome
NSW: new swappers welcome
SASE: self-adressed stamped envelope
SNNP: sorry no new pals
SNNS: sorry no new swappers
W/W: worldwide