There are several places where you can find sources for your paper. However, you want to keep in mind the following considerations when looking for sources to use in your literature review:
For example, if you were looking for an article on tablet apps for early childhood education, you might find an article that completely focuses on the use of apps in early childhood education as well as one that only has a sentence or two about apps in early childhood education. The second one would probably not be very useful for your literature review.
It definitely should!
Does the author have the education and experience to discuss this subject? Is this person's work cited often in this subject?
Though good research can be found in low-impact journals (journals that are not cited as much as others) and books from small publishers without much of a reputation and bad research can be found in high-impact journals (journals that are cited often) and books from highly regarded publishers, the reputation of a journal or a publisher does matter in the scholarly world.
If you see an article being cited over and over again in the bibliographies of works you find, you should look at it.
I recently looked at Apple Classrooms for Tomorrow research. This research was funded by Apple Computers and, not surprisingly, the outcomes of the study were largely positive. While there is a lot of research that is funded by organizations with an agenda, this does not mean that you should necessarily eliminate it from your literature review. However, you should examine the research for flaws or omissions resulting from bias and include that analysis in the literature review.
Your instructions will determine how far you need to narrow down your topic. You need to narrow down your topic so that you don't ramble or take on more work than you can possibly do or than the assignment requires.
My topic is too big.
Your topic should be humanly possible for one person to study. If your topic would take yours and many others' life work to research adequately, then you should probably narrow it down. One example of such a topic would be at-risk population. At the very least, there are thousands of resources that address various populations. But if you narrow your topic down from at-risk populations to Latina girls, you will have a much smaller and more manageable set of results to look at. If you're not sure what you want to narrow your topic down to, search for and read some materials that include your broad topic. These materials will focus on a different smaller aspect of the topic. For example, if you just searched for at-risk population, you might find results about LGBTQ teens, justice-involved mothers, children from low-income families, and the list goes on. While you review your results, you are bound to find a topic that is manageable to search for.
Don't know if your topic is too broad? Search for it in one of our education databases (try this a few times with different keywords; sometimes there is more research on a topic than you know, but you didn't search for the right keywords to find the information you need). If there are more results than you can reasonably be expected to look at, then your topic is too broad.
My topic is too small.
Sometimes your topic may be too narrow or give you few results when you search for it. This may happen if your topic is ultra-specific, i.e. pregnant Latina teenagers with depression in Richmond County, GA. If that is the case, you may need to make your topic broader (perhaps focus on pregnant teens with depression or Latina teenagers with depression ) or pull on research that addresses some piece of your topic (e.g. looking at both pregnant teens and Latina teens and make the connections yourself).
My topic is just right.
Now you can move on to organizing and analyzing your sources.