Tom Waits. I’ve loved Rain Dogs for years but barely scratched the surface of his other stuff.
The Fall. Where the fuck you supposed to start with that. Actually i don’t think I want to be into them
Mexican folk music. Not like mariachi bands. Like, I dunno. Heard a couple of songs here and there but know how to find more.
The Glitter and Doom live album is great and might give you some jumping off points for other albums to try.
Vic Chesnutt
Zappa, Beefheart.
Try Mule Variations for Waits, incredible album which showcases his range. If you want his jazzier early stuff Blue Valentine is a good one.
I’d suggest clear spot for beefheart. Some of his most accessible (and best) songs, but with enough weird stuff at the edges going on.
Zappa - start with Apostrophe and Hot Rats. Hot Rats is largely instrumental (but one track features Beefheart!), and it’s full of joyous yet insanely complex arrangements. And the song with Beefheart rocks. Apostrophe, on the other hand, is more representative of the rest of his work. It’s driven by a half-sung, half-spoken narrative full of strange jokes (but with some VERY catchy moments), but as it’s not as long (or as grotesque) as some of his other stuff, it’s the perfect place to start. And again, the title track rocks.
Beefheart - just listen to Safe As Milk!
Pretty much what I was gonna suggest. If you want accessible Zappa you could also try Overnite Sensation, Zoot Allures or One Size Fits All. But Hot Rats was the first one of his I loved and now one of my favourites ever, so probably just go with that.
Anyone got good metal recommendations for someone who likes Sabbath and sludgy rock but never managed to bridge over into the proper stuff? is there some sort of mindset which helps appreciate it?
Other people will be better placed to help you here, but it would help if you specified what you mean by “the proper stuff”. Because as far as I’m concerned, Sabbath and sludge ARE “the proper stuff”!
I dunno, metal classics…stuff from the metal section in record shops. Or just more sludge/doom recommendations for a beginner I guess
Metal is such a broad church that it’s difficult to post general recommendations, but if you like riffy, sludgey stuff then I’d recommend Melvins. They’re not the canonical albums, but I got into them through The Bride Screams Murder, Nude with Boots and A Senile Animal.
Boris are worth a listen too (named after a Melvins song). Maybe try Pink to start with and go from there.
If you want more tunes with your riffage, then anything by Torche is good.
King Gizzard & The Lizard Wizard
If you like Rain Dogs definitely also listen to Swordfishtrombones, as it’s the same era and very similar. Nighthawks at the Diner is cool in more of a jazzy, bluesy, faux-live feel thing way. I also really like Bad As Me, his latest.
Zappa – as people have said Apostrophe and Overnite Sensation are accessible and brilliant, and Hot Rats is probably his masterpiece. We’re Only In It For The Money is a bit more strange, but songs like Who Needs The Peace Corps are brilliant.
Nonagon Infinity
I haven’t heard nearly all of his albums so someone better versed in his whole catalogue might say otherwise, but I think “Is the Actor Happy?” is a good starting off point, personally.
give yellow & green by baroness a listen. great album but not as heavy as their earlier stuff so probs a good entry point
I don’t know much about Mexican folk but you might like Jorge Cafrune, he’s Argentinian but might be similar to what you’re looking for
Keep meaning to get into Prince, the good years…
Growing up he was obviously something of an ever present, but around the time that I started to get into music seriously was when Diamonds & Pearls came out and that felt a bit like the first time that his quality control slipped and therefore put me off him a bit. Plus I would liked to have seen him live and that’s not happening now 
Any tips? Should I just start at the beginning and listen all the way up to and including Graffiti Bridge? Any late career classics out there?