The preprint services listed in the box below are useful when considering the quality of the article you are thinking of using. If an article has gone on to be published in a peer reviewed journal, comments on the preprint server will give you an idea of the strengths and weaknesses of an article.
Check for editorial comments or retractions in PubMed, or other databases. Some comments may make you reconsider using an article.
Another way to find out more about the quality of an article is to search for it in PubPeer. PubPeer allows people to leave anonymous comments critiquing published articles. In some cases, these comments have led to reatractions and ethical investigations.
For basic literature reviews, these steps are not crucial. But for a dissertation or thesis, you should be sure to follow any links you see to commentary. Especially if it is a research method you are using to do your research.
There are many resources that do not make it into the peer-reviewed literature found in most Library databases. Some databases, such as Scopus or OneSearch, can help find books and book chapters. The list below includes sites to search reports from government and non-governmental funding agencies, preprints, clinical trials, and government awards. Any of these can help you find more materials on your topic.
PRISMA ScR - PRISMA extension for scoping reviews http://eprints.whiterose.ac.uk/136633/ paper, Checklist
Cochrane training manual https://training.cochrane.org/handbook/current (more than needed in most cases, but it can be used to learnmore about each step)