Summarize:

When creating new words to describe fictional settings, take your theme and tone into account. Your newly created words should sound natural to the world that they inhabit. Foreign words can help to foster atmosphere, depending on the language: Germanic languages are rough sounding, and have a guttural feel to them. Using Germanic-based words for tough characters can make them sound hardy. Using Germanic language for evil characters will give them a bestial quality. Romance languages are light and airy, and can give your characters a seductive quality. Naming locations with a French- or Italian-based word will create a sense of exoticism. Use Latin-based words to add a scientific feel. Latin evokes wisdom, and so Latin-based words can also imply intelligence. Latin is also an ancient language, and can be used to add mysticism. Asian languages make good base words for exotic sounding locations and objects. Use other languages as a basis for the sound and feel of the word you are creating. Avoid copying a word directly and instead use it as a guide. A successful word is one that the reader won't trip over too hard. Try to relate the word to some recognizable concepts. For example, using the made-up word "bogmouth" to refer to a mouth condition gives the reader a general sense of what the character with bogmouth is experiencing. This is because the word "bog" is familiar, and evokes a similar feeling in most readers. Writing out an official definition for your word will help you to use it properly. Format your definition as it would appear in a dictionary, and list out any other forms the word can take. This can be especially useful if you are writing a piece with multiple made up words, both as a reference for you and for your reader. If you want your new word to stick in the readers' minds and become second-nature to them, it needs to appear multiple times in your writing. Studies show that readers will understand a new word after reading it ten times with context. This means that your word needs to be supported by the language around it to provide the reader with clues on how the word is used and what it means.
Identify your theme and tone. Make a word that is recognizable. Define your word. Repeat your word.