When I first started to learn Chinese, I did so without a teacher. I listened to tapes and many other mediums to try to learn the language. Because Chinese was so different from English, I developed bad pronunciation habits. When I finally got a good teacher, I had to unlearn the bad habits before I could learn the correct pronunciation. My advice is to listen and imitate as much as you can, but also seek out a native speaker that would be willing to point out any pronunciation mistakes.
Sandun81 is correct about vocabulary. You must read, and read a lot. However, you must do your best to find materials that are at your level. You need to read at least 1 hour every day, and you should understand 95% of the text. For extensive reading, you don't want to be stopping every other word to find the meanings. Instead, you want to be able to find the meanings in context.