|Avoid the vertical learning curve.|
You'll lose your audience before your
story makes it off the ground.
Every book has a learning curve. Whether it's fantasy, science fiction, historical, or modern-day thriller, every story has information in it that readers will have to learn in order to understand or fully appreciate it. How quickly should an author deal out this information? I've read books that do it every which way, which means there isn't a right or wrong way to do it. There are benefits and problems, however, no matter how you do it. Here are some examples:
Harry Potter. J.K. Rowling is a great example of how a writer would ease an audience in to a fantastical world. First of all, she begins her series with one point of view character. One boy, living in a normal world, with a boring life, and a few family members with easy-to-remember names. Her story, of course, is about an entire magical world hiding in plain sight, and so she introduces readers to said world a few steps at a time. By the time Harry reaches Hogwarts, we're totally sold on the world. We don't know how it works just yet, but she hasn't lost us with any difficult terms or concepts. By the end of the series, she has taken readers much deeper into the fantastical, introducing things left and right that we are expected to keep up with. Rowling uses the gradual curve to great effect.
George R.R. Martin is another household name in fantasy, so let's talk about his great epic, A Song of Ice and Fire. Martin's world starts with a much steeper curve than Rowlings, but he is writing to an adult audience, most of which have already been reading thick fantasy novels by the time they pick up his work. So is his curve a huge one that readers should be scared of? I don't think so. Yes, there are a lot of names and places mentioned in the beginning of the series that you'll quickly lose track of. The thing about his series, though, is that all of the important world information is repeated so many times that by the time you need to know it you've gotten it all down. What Martin does is brilliant. He has this huge world, with a large cast of view-point characters, but he starts all of the pov's--with the exception of one--off in the same location. This way, we are introduced to a lot of people, but they keep referring to each other and it is easy to keep up. Martin's curve will be steeper for newcomers to epic fantasy, but fairly normal for those who have read the genre before.
Steven Erikson is the best example that I've come across of a writer with a ridiculous curve. I think his is very nearly vertical at the beginning. If you want to know what I'm talking about, open up Gardens of the Moon--the first in his Malazan Book of the Fallen series. I've been reading epic fantasy for more than ten years and he lost me on that one...
Now you can get a feel for what I'm talking about. So, what are the pros and cons? A gradual curve will make it easier for readers to digest. It will probably mean you'll have a wider audience, which can translate into major success. The gradual thing has been done to death, though, and so experienced readers might roll their eyes and not give your "simple" story a try. If the learning curve is significant you can deliver a world that feels completely real--every corner can be fleshed out, every character explored. You'll probably have some hard core fans that will defend your story with their own blood. That hard core group might be small, though, and so your book could be great, but not widely read. Really, it's up to the writer to decide the type of story they want to tell, and then tell it.