I can answer that from announced cast list already. Nereus is in it. I'd like to see Murk, Tula, Urcell, Jurok Byss, Garth, Dolphin, the Idyllists, King Shark, Arion, et cetera, however, it already looks like the movie is being ambitious enough to introduce us multiple underwater races, The Trench, Orm, David Hyde, Vulko, Atlanna...Wan has too much to introduce already.

And really, almost all of those characters aren't obscure as long as you've read three Aquaman books, tops.

I haven't read any. Are they worth it? In the JL comics I've read, I've never really liked Aquaman.

Do they have Aquaman: The Drowning at your library?

I assume I can get it. Is that a good place to start?

It's the book that made me realize how much of a badass Aquaman is. It also directly discusses the "the guy that talks to fish" trope.

That's where I'll start then. Any other good arcs or series?

Ask Grimm; he's the expert. (There's an Aquaman by Geoff Johns Omnibus coming out this December, though, for a really good price on Amazon!)

The Johns, David, and Abnett runs are my favorites. Although the only Aquaman comics I haven't really enjoyed are the Showcase volumes covering the late fifties and early sixties. I still like the art in those, though.

Either Geoff Johns run (beginning with the Trench), or Dan Abnett run (technically begins before The Drowning, but...) are good starting points.