Speaking of Generations, which episodes should I watch before that?
You might want to check out Redemption 1&2
for an introduction to Lursa & B'Etor
I mean this facetiously (for the most part), but you don't really need to know anything about Lursa and B'Etor other than that they are Evil Klingons Who Want To Destroy The Enterprise™. I mean, yes, TPTB deserve credit for using previously established villains, but their choice in that respect leaves something to be desired in my opinion.
But, yeah, "Redemption" is a great two-parter, so you should watch it anyway.
(And it is a thoughtful suggestion in any case.
Honestly, I think a better use of "background episode" time would be to watch something that introduces you to Guinan and her Intuition. I think "Yesterday's Enterprise" would be good introduction in that sense. (And it's a killer episode in any case.) Understanding her character as she appeared in the series makes her role in this story more poignant, I think.