If you want to create a realistic science fiction/fantasy world, language helps a lot. Here are some conlang (constructed language) resources for creators and those interested.
How to write the next great alien language (io9.com on J.R.R. Tolkien’s Elvish and Marc Okrand’s Klingon)
Linguist Marc Okrand on how he used less common sounds/grammatical forms to make Star Trek’s Klingon language more alien: