Whenever you write anything that is intended to convince, inform, or advocate you should think about your audience, and the type(s) of sources that audience finds convincing.  For many of the papers your write in school, your audience is an academic -- a university professor.  

As a student, you have one major advantage -- your audience is readily available.  If you have questions about the types of sources they would like to see, you can (and should) ask!

This is especially true when you are writing in an unfamiliar field.  Different disciplines have different expecations when it comes to evidence. Don't assume that because you know your way around scholarly sources in one field, that another field will work the same.

Here are a few general principles to guide you: 

The goal of academic argument or discourse is inquiry.  

    • Your professor probably wants to see that you can evaluate an issue thoroughly, from multiple perspectives.  Your sources should show that you have done so. 

Inquiry means that there are always more questions.  

    • To academic audiences, the best sources are the books and articles that other people use to generate new questions and new research.  
    • If you see a source mentioned a lot by other sources -- that's probably an important source for you to consider.

Academic audiences are likely to find conclusions that are based on rigorous, carefully conducted research the most convincing.  

    • In most fields, research is primarily reported in peer-reviewed or refereed journals.  
    • In some fields, you will also find research in government publications.
    • And in some fields, particularly in the arts and humanities, you will find a lot of it in books.

The credentials and authority of the author are also important in academic discourse.

    • While it is true that anyone can do good research, someone who is affiliated with an institution known for good research will often get extra credibility.

In many fields, there is general consensus about the "best" or most important journals and publishers.  

    • Research reported through those channels is automatically given more attention.  
    • As you progress through your major, it is a good idea to find out what journals and publishers are important in your field.