Researching German Ancestors

Although I have German ancestors, I haven't done a lot of research into my German ancestors, when it comes to German records. So far, I have only been able to trace a couple of branches back to their town or village of origin. Before I go any further, I must state that a family tree had been done previously on one of the families. I am still going through and reconfirming the information since I don't have the original researcher's notes, and I do not know what records he used. I must also mention that in going through the data, I have come across errors, especially when it comes upon information on people who lived in the United States. The errors are exactly why I am going over the information, and the arrangement of the branches make determining relationships very difficult. The tree is completely in German, and even though that is not a major problem for me, there are German words that I have come across that I can't find in my German dictionaries.

So, what have I done to confirm or disprove the information on the tree? I have used obituaries, passport applications, passenger ship lists, marriage records and death certificates. Of course, this isn't an exhaustive list, but as I am still working on determining where most of my German ancestors came from, I'm still looking for more records.