I usually watch anime dubbed if it's from the 80's or 90's, even if the dub is terrible, because it's nostalgic. Otherwise, I go by setting. If the anime takes place in japan, I watch it in japanese, if it takes place in america or a random western-ish fantasy world (like full metal alchemist or trigun), I watch it in english
I've just picked up some words from watching anime every day for the last ~6 years.
if there's ever a word you want to know, try googling it. like, if you wanted to know the word bicycle, google "bicycle in japanese" and it will tell you how to say it and give you the kanji