There are a number a websites that teacher librarians can search to find ideas for teaching students how to choose the right books.
This teacher librarian blog has multiple links to help students choose books. It also has lesson plans.
http://inquirytecheastman.blogspot.ca/2010/11/choosing-books.html
A video that helps teach students how to pick books for themselves.
http://www.brainpopjr.com/readingandwriting/readingskills/choosingabook/preview.weml
Click on this link to get a printout for the classroom.