http://www.eslprintables.com/writing_worksheets/story_writing/Science_Fiction_Story_Writing_89472/#this
http://www.eslprintables.com/printable.asp?id=383614#thetop
http://englishtips.org/1150886624-writing-science-fiction-fantasy-horror-how-to.html
http://englishtips.org/1150812184-writing-fantasy-and-science-fiction.html
http://englishtips.org/1150802880-the-craft-of-writing-science-fiction.html
The books are for older students, but you will find some useful things in them.
Good luck!
Julia