Immersion, it's said, is the fastest route to fluency. Surrounding yourself with Spanish speakers and promising yourself you won't slip into English is one type of immersion; complement it with some literary immersion, too.
At La Torre de Papel, you can pick up Spanish-language magazines, books, and newspapers, not only those published in Mexico, but others from South America and Spain.
You might not understand every word, but you'll inevitably enrich your vocabulary. Plus, the multiple forms of exposure to the Spanish language will likely help you begin to feel more comfortable speaking it, too.