Like in English, you can either sound like a normal person or like an idiot that is trying to imitate some slang. I recommend to learn "real" German. In everyday speech, we prefer shorter sentences with a few subordinate clauses. But you can only use our grammar correctly if you know the grammar. For instance, we've got two past tense forms: Perfekt and Präteritum. While in written German "Perfekt" is the correct past tense for "Präsens" and shouldn't be mixed with "Präteritum", we tend to use both in everyday speech. It depends on what is easier to pronounce and what sounds best. There's almost no "right" or "false" in everyday speech when it comes to the tenses. But the word order has to be correct. If you don't know any German, visit "Nachrichten leicht" ("News easy"). That language is actually for disabled people. Easy words and sentences with – in terms of (written) Standard German – grammatical "errors" you can use "in the street". I think it might be helpful for you because you can read and listen at the same time. http://www.nachrichtenleicht.de

I am learning German too. I'm a beginner and I'm working in my pronunciation. I found a YouTube channel that has a "Friends style" series in German: http://m.youtube.com/watch?v=yhP3OT2hxAE What's special about them is that the episodes have German subtitles. I find this very useful to understand words and pronunciation while learning spelling and uses for the words... I don't know if I am making myself clear...

Just as in English, there's a wide range of styles in German. And just as colloquial English is different from written English, colloquial German is different from written German. It's certainly "useful" to be able to use both styles in the appropriate situations. If your main focus is on colloquial spoken German, then watching movies will be more helpful than reading books, of course.