|Image of a dump at Fadiouth, Senegal from Wikipedia.|
Originally taken by John Atherton.
It only takes a morsel to convince a reader you know what you're talking about. If the purpose of your book is to generate interest in a subject, the way to teach them about it is not to inundate the reader with information (unless you're writing a nonfiction book about it, in which case, carry on). The more you throw at the reader, the less the mystique.
You have to trust your reader to have a brain. That brain will either recognize that you know what you're talking about, or it will be intrigued by the tidbit of information and want to learn more. Dumping it all on your reader right then and there is patronizing, and it brings the narrative to a screeching halt. If you're doing it at the start of your book, you've given the reader a reason to put it down and go read something that isn't talking down to them.
Infodumping can also be delivered in the form of world-building. Your world must stand on its own, without every aspect being explained as you go on. Readers will pick up a lot from context. You can sprinkle in a few sentences here or there to offer some context, but there does come a point in time when you have to stop holding the reader's hand and trust that they'll follow you into this strange land you've created. If you don't, once again, you've killed the pacing, and you're talking down to your reader.
I can't give you an exact formula of how much information to include, because that will depend on the story and the world and the concept. The best rule of thumb I've heard is to cut anything that isn't immediately required in the narrative. If it doesn't play a part in the story, out it goes. Also, it should be sprinkled liberally. More than one paragraph of information per scene is probably too much, and should be spread out more evenly. If your beta readers or crit group doesn't remark on it, though, you're probably fine.
Just try to be aware of whether you've put in a piece of information because it's vital that the reader know it, or if you thought it would be fun to include. If it's not vital, out it goes.