Academic Content is an important part of figuring out what it is you're going to teach, but as a teacher, one can't be too worried, simply because there's a curriculum that you need to follow that varies from school to school. That being said, you should also have the help of fellow teachers teaching the same subject to depend on for when a certain test should be done by and so on so forth. With that information, you can gauge the development of your class and figure appropriate lessons based on the time you need for them to be ready for that big test we all love so dear.
Try: Read/Write/Think (LA)
Illuminations (Math)
Science Netlinks (Science)
or Smithsonian's History Explorer
(Transforming Learning with New Technologies, 2nd edition, p. 75)
And what are some ways of doing so?
When considering what lesson you want to plan, there are websites that can help you do just that based on the curriculum that you're trying to teach.
When thinking of a lesson, one must take the entire classroom into consideration, for Ino might have issues or learn a certain way that Bill doesn't learn. This is why, typically, the first week of school is a "get to know you" week, so that you know what your students are capable and incapable of. From there, you take a basic skeleton on what a lesson should look like, and you expand on it via adlib, or specific plans of teaching that caters to every student.