I recently read a post on Lawyerist entitled Building Your Vocabulary Can Hurt Your Writing. It's a quick read, but I'll summarize the basic point. Using obscure, "highfalutin" words for the sake of showing off your vocabulary will hinder the clarity of your writing, not improve it. Writing well is not an exercise of plucking complex words out of the dictionary or thesaurus, as if you're ordering sample platters off of a restaurant dinner menu.
There is a reason for this, for which I find to be intuitive and obvious (though others may not think so): you are what you read. If your spare time is spent reading People and US Weekly, then you cannot expect your writing to improve. Read nothing and expect nothing in return. Your writing ability may even deteriorate On the other hand, a lifetime spent reading good prose - whether it be classic English literature, a current events periodical, or even just a newspaper editorial - is a lifetime spent listening to the music of language.
Put it this way. On the SAT, I scored much higher on the verbal section than I did on the math section. I was never a great numbers person, but neither did I think I had the most proficient verbal skills (In fact, I still think there is always room to improve one's writing, regardless of skill level). I did, however, spend a lot of my free time reading books with fairly refined prose. I wasn't reading Dickens, Shakespeare, or Macaulay, but I did read my fair share of fiction and non-fiction, anything from Hemingway to an acclaimed political biography. As a result, I gained an ear for good writing, and, in the process, internalized the techniques the great writers used, and how they would use just the right word, or vary the length of their sentences just so, to convey a specific idea.
To my mind, there is no substitute for reading well. Otherwise, it's garbage in and garbage out, which is why in today's digital world you read tweets like this.