Look up a textbook for a general lesson plan/structure and try to base your lectures off of that outline. Textbooks generally keep it simple at the start, so try to follow that as well (for example, in the beginning you might just base everything of static methods and the main method). As far as what static or public mean, tell them not to worry about that now, but just focus on getting them to use Java basics like if, for, while, system.out.println, etc.

Also, have your lectures for each class completely planned out (write up a complete set of lecture notes) before your start the class. Don't try to improvise a lecture, as it will not go well.

Students learn by doing, so give them plenty of example problems in class to reinforce concepts. As far as how hard in class problems should be, you'll get better at judging what is easy/difficult as you teach the class.

I've found that for anything even slightly difficult, giving the students plenty of guidance before asking them to program helps. For example, I will start off by clearly explaining the exercise. I then will prompt the students to say what they need to do, and get it in list form. For example, I might say "we'll need to store 5 integer values, how should we do this?". A student will reply "create an integer array", and I'll write that down. Then I'll move on to the next thing they will need to do.