I'm just parroting Donnie here, but for the love of Ogdru Jahad, if you've never read Hellboy and are interested ignore that Mignolaverse reading order nonsense. If you wanna check out Hellboy start at volume 1 and then keep going volume 12 and then read the two volumes of Hellboy in Hell. That's it! If you want more, then you're in luck because there's a handful of OGN's that fill the gaps in his history. You never have to touch BPRD, Abe, Lobster Johnson, or any other of the related books unless you're so inclined to explore more of the that world.
You can do the same thing with BPRD if you're not as keen on HB, but are interested in the larger world. There's four big Plague of Frogs volumes, then a big 45-47 volume, a couple of one offs, and then 15 volumes of Hell on Earth. If you wanna know what Abe gets up to, then guess what, he has his own book that spins off of BPRD! But at no point do you need to read the former to stay caught up with the latter.
That reading order does the books such a disservice because it makes it look like you need to read 3 volumes of 1 thing than alternate between 2 different things before throwing in a 3rd. And you don't need to do any of that, you can just read them as they stand on their own.