Lots of great information has already been said, but considering my occupation, I thought I should make mention of some things. The real key to acquiring a language (first language, second language, ...) is input. Input is listening and reading. It is especially important when the input is able to be understood by the receiver (i.e. comprehensible). The suggestions for books you are familiar with, music you know, and church services are fantastic exercises for acquiring a second language because the input will be comprehensible. Blaine Ray readers are pretty good (
Blaine Ray Workshops, Inc. ) because the texts are comprehensible for even the most inexperienced readers. I would certainly look at a grammar book or spanish grammar websites like studyspanish.com in order to advance more quickly. The key, again, is input - reading and listening. It is how we acquire our first language and how we acquire a second language.
Just an aside I wanted to mention that, as a high school Spanish teacher, people always say things like "I didn't learn anything in Spanish in high school" or "I took x years and I don't know any Spanish." Again (and I know I'm being repetitive here), it was because you didn't get enough input from those courses. Think about it. How much acutal Spanish was spoken in that class? Usually it isn't much. Lots of worksheets, writing, paper mache piñatas, etc. Probably not enough input.