Each year I decide upon ten different genres to highlight throughout the year. I assign a different genre to each month of the school year and celebrate that genre during its special month. There are no hard fast rules for which genre should be presented at a given time, but I typically make October supernatural/scary as it easily connects to the Halloween theme.
At the beginning of the year we start off by having a discussion of genre and I let the children brainstorm a list of genres they are familiar with. After compiling a list on chart paper, I explain that each month we'll feature a different genre and that they should try to read books from that specific genre each month. Sample genres to choose from include: fantasy, science fiction, realistic fiction, nonfiction, humor, poetry, autobiography, biography, supernatural, religious, mystery, or inspirational.
During a given month I make sure that my read aloud material connects to the theme and that I pull out a variety of books from my library or the public library to have on hand for the students to read from. Having a genre of the month also lends itself to Writers Workshop as you can model various writing projects in connection with the theme and challenge children to write their own stories that fit into the genre. Likewise, for those teachers who assign monthly book reports, there is no better way to assure that children try books in various genres than to formulate the guideline whereas their book reports have to connect to the monthly theme.
Each year I design a bulletin board display that stays up for the entire year. I design it in web format with the genre of the month featured at the center and descriptions and features of that genre highlighted in the various branches. To add flavor to the display I photocopy the jackets of several books in the selected genre and hang them up around the web.

Happy Reading!