The English language is constantly evolving, with new words added to dictionaries and others falling out of favor. Sometimes new technology or scientific breakthroughs dictate these new words (i.e. podcast), other times they evolve from use in popular culture (i.e. hoodie, crunk).
There's certainly a precedent for writers inventing words. Shakespeare is credited with the first mention of roughly 2000 words in the English language, many of which are said to be of his own invention. Lewis Carroll's poem "Jabberwocky" is filled with nonsense words, some of which have found their way into familiar usage. Carroll's invented word "chortle," for example, is made from blending two words that already existed: "chuckle" and "snort." (Such blends are called portmanteau.)
But before you start stringing syllables together to make new words, consider your motives. If there's already a perfectly good word that captures what you want to convey, then it makes sense to use it. Purely invented words often don't have a long life and some don't ever catch breath because they just don't carry a recognizable meaning. You want your use of language—and what it conveys—to last.