Over reliance on too few sources can lead to plagiarism. You can get trapped inside the world view of a few academics or researchers and become their intellectual prisoner.
Don't base entire assignments on only one or two sources. Read and research more widely.
Better research provides a broader scope of ideas and interpretations to draw on. This also requires greater integration skills on your part. The more sources you use, the greater skills required in their blending. The fewer you use, the more likely you are to accidentally plagiarise by taking too much from one source.
Learn how to find and evaluate information for your assignments.