Hit up a library and get reading. There's nothing worse than a teacher who puts up scans and readings but cares less about the subject than the students. Find someone you love about American History that you think students might never learn anywhere else and pair that up with some basic foundation history. How and why there is a Declaration of Independance in the first place etc.. There are going to be a couple kids in your class DYING to learn from you. It's important you steep yourself in the content you're teaching.

If I were you, then I'd focus on a concise narrative chronicling relevant historical developments which contribute the most to our current circumstances. Help explain the world they live in through historically relevant developments. What is the point of talking about the history of the United States if you're going to end the lessons.. the story of your history class.. on some 'america is great' propaganda or 'the indians died and now we're all american - class dismissed' tripe?