I agree with the last 2 posts. Grammar is tough in general, but books are the fix. I would go for an actual book to read and then the same book to hear. The more you read, the easier it is to recognize sentence structures and constructs, and after you read you will be able to hear the same sentence structures from the audio books (as CJ points out). If possible get something that you really like. The news is also good as wayne points out to hear it, but the news a lot of times included popular culture terms that aren't exactly grammatically correct. ¡buenos suerte!

listening to english audio books can also help. I believe the quickest way to learn grammar is threw sound. Thats how we learn our own language, wend we are babies listening to our parents.

I think you will improve greatly if you practice everyday. Try reading newspapers published in English, watching television programs that are broadcast in English, and of course speaking with people who speak English as much as possible.