Okay now I feel bad for making him sad.
Seriously though, there's no magic advice in this game or a secret that someone can tell you that suddenly improves your physical abilities.
It's like asking how to run a marathon without getting tired or lifting serious weight without any practice. No words can help you there, just keep playing the game.
Look at people like Toy, rrtyui and WWW and check how many hours they've played and how many times they've played that map and you'll get why people are acting the way they do.
Also, that's like the most stereotypical thing to ask and play at your level. I get that the map is osu culture and it got many people into the game but it's still a 6.35*~, and more or less, shitmap.
The reason you passed ILY is that ILY is basically a 7,4* 220BPM Choco cookie, and you have practiced modern map jumps by playing it all the time. Big Black is some old meme map that's mapped entirely different and awkwardly which is why it's "hard".
If you wanted to practice for it, you'd have to play Blue Dragons / Mismagius other stuff, most of which is equally meme and difficult, so you can't really practice it on your level.
Tbh you're better off forgetting about that map and come back to it when you're 5k-7k pp and AR10 is ez for you. If you want to pass an iconic map that might be doable at your lvl with some practice, try Scarlet Rose instead.
One thing you can do to speed up the process is playing Big Black with HT every now and then to learn how the patterns work and are meant to be played, so you have an easier time hitting it when you try to pass it sometime later.
Edit: Yes, you are overranked.