Labels - mail-merged from two spreadsheets, one for UK addresses and the other The Colonies.
And when I have used all the labels I have printed - I know I'm finished!
I received one card addressed to the right house number, the not-quite right street name, the name of a Welsh Village, "S.Wales", and a non-existent Post code. Well, I crossed out "S. Wales" and substituted the Post Town (in capitals!) "CALDICOT" (Never heard of it, but still ...) and tacked on the appropriate Post Code, and shoved it back into the post.
I think I live about 190 miles away from Caldicot! Oh and I still get cards addressed correctly except the address includes the county we used to be in forty years ago.
I can recommend free software from Avery, called Design and Print, for labels and mail-merging - it can be a bit of a nightmare to do yourself, but the application makes it a doddle.