Expository writing as I understand it is nonfiction writing. I teach it as steps. Ex: Get ready for school. First get dressed. Next eat breakfast. Last brush your teeth. Or you could do how to eat breakfast, sports kids could do how to play...etc.
I am teaching beginning, middle, last right now. I took a piece of copy paper for each student and cut it into quarters. Staple it together on one side to make a mini book. This will show how the supporting sentence (one on each page-put it together later as a paragraph) goes with the main idea sentence (on the first page) and let them draw a picture with it. I tell the kids they get to be authors of book just like the ones we read in class.
You could also use a bubble map to show how the supporting sentences go with the main idea sentence (in the bubble in the middle of the map).
I am required to teach expository and narrative, so yes this is typical requirements for first grade.
Here is a website that might help: http://www.kidskonnect.com/content/view/350/27/
I hope this has helped. Good luck!