These are some common mistakes students make--avoid these and and your paper will be both better and easier to write.
1. Avoid choosing a very specific topic and starting to look for sources. Sometimes a narrow topic idea does not have a lot of information published about it., which will make it hard for you to complete your project. If you look at more general topics first, you'll get an idea of which narrower topics will have research published on them.
2. Avoid looking for primary articles immediately. If you don't understand how the primary articles relate to other research being done in the same field, you'll have a hard time knowing which articles are pertinent to your research and which are not. Read secondary literature first so you won't end up writing a paper using articles that aren't well connected. It may not always be obvious to you when this has happened, but it will be obvious to your professor!
3. Avoid citing sources that are intended for patient education. The information in these sources may be relatively reliable, depending on the source, but they won't explain in detail what methods were used in research, or how scientists came to specific conclusions. When you are writing a research paper, you need to include that information.