I have found that examples can be one of the best teachers...
I give my students this sample of a "paper" that not only shows them how an MLA-formatted paper should LOOK, but instructs them as well. It addresses in-text citations, how to punctuate these citations, and has a works cited at the end.
This is a handy resource for students, and something that they will refer to often throughout the school year. It also makes life easier for the teacher - you can tell them to refer to the sample paper instead of answering (for the hundredth time) what font to use... :)