From a college student and future English teacher:
You should have a title page with the title of your paper at the top, your name, your class's abbreviation, and date much lower than that.
Your paper should be formatted like this: 12pt font, Times New Roman, normal margins, double-spaced. You should cite your sources as your professor has requested, and if they haven't said anything or expressed a preference for MLA or APA, use in-text citations and a Works Cited page that conforms to either MLA or APA standards.
Purdue's Online Writing Lab has helped me beyond belief:
http://owl.english.purdue.edu/
My advice? Add block quotes AND FORMAT THEM CORRECTLY. Not only do they take up a lot of room, but professors love to see that you correctly cited all of your sources. The biggest problem I see in academics is either 1) either not citing correctly or enough, or 2) not providing enough evidence via good quotes and citations.
If your paper is too short, the likelihood is that you haven't provided enough evidence for your argument.