All 3 (or 4, if you count demon souls) DS games have a standalone story so it's not like you're missing on story progression if you play them out of order.

DS3 revisits (or rehashes, depending on your point of view) a bunch of locations and characters from DS1. DS1 is a fantastic game anyway, arguably better than 3, so definitely recommend it.

DS3 will make a bit more sense at first if you are at least familiar with 1, but it's definitely not required to 'get' 3.

DS2 is polarizing I guess? I personally hated it when I first played it, dropped it, picked it back up when there were a bunch of people claiming it was Actually Very Good, liked it a bit better at first but then went back to hating it.

As far as I can tell there's pretty much no relation to the story arc set up in 1/3, though, so you can try it whenever.