Here's how I started by boards this year. I like to set up a back ground that I can use throughout the year.
Usually the information on my walls and boards is supplementary and not kept current for the material we cover in a single unit -I would have to change them out too often! That being said, I do think it is super, super important to change the information on your boards several times throughout the year. This shows the students that you are interested in their education, your mindful of your surroundings and you care what your room looks like.
(This is another spot in the room...the kids refer to the map of the USA all the time.)