Science fiction and fantasy generally require more world building than other genres because you have to build a world separate from the one we exist in, or at least insert some new element that plays a significant role for the story. I have seen this challenge lead to excessive exposition, especially early. I'm reading a book right now that I probably won't finish that built an interesting world but is guilty of excessive info dumping in the first few chapters (among other issues).

What works have avoided this particularly well and how do you avoid it?