Exposition, or the explaining of things, is a tricky part of any genre, but with speculative fiction it presents some unique challenges. You've created a whole new world here. There is so much that the readers won't know about it and need to understand in order to get the story, right? History, customs, culture, magic systems or advanced technology, not to mention all the back story that brought your characters to the point where the story starts.
You may think it's necessary to dump all this information on your readers right up front, so you can get the story going once they're up to speed. Not so. You must resist the urge to info-dump on your readers. Nothing kills a story dead quicker than opening with a bunch of exposition and no action, characters, nothing.
There are better ways to handle this dilemma. I've discussed some of them in a previous post, if you'd like to see some specific ideas. It's a fine line to walk, though, because you also don't want to leave your reader with too little information to figure out what's happening. You have to learn the art of dropping in tidbits here and there, like bread crumbs on the path. As I mentioned before, speculative fiction readers like to discover these things for themselves without having it spoon fed to them. It has to be handled with finesse, and the best way I know of to learn how is to read a lot and to practice a lot. The more spec-fic you write, the easier the exposition becomes.
Do you have any favorite techniques for imparting information to the readers?