The peer review process ensures that articles submitted to a journal are subjected to a review by subject experts prior to publication. Some library databases offer a feature that can limit your results by peer reviewed publications. Keep in mind that it is possible to retrieve a poorly written commentary from a high quality publication.
If you are utilizing a database or tool that does not offer this limit, you can use Ulrich's periodical dictionary, also available on the Health Sciences databases A-Z list, to determine if a journal uses peer reviewers (or "referees").
When using the internet, consider these 5 points to help judge the quality of information.
Currency/Date: the timeliness of the information
Relevancy/Coverage: the importance and scope of the information
Accuracy: the reliability, truthfulness, and correctness of the information
Authority: the source of the information
Purpose: the reason the information exists
For more, see the CRAAP Test
Primary sources are those that are a direct report by the author who was involved in the research or experience and is reporting the results shortly after completion. Emphasis should be on relaying facts with minimal analysis. Primary source designation does not necessarily indicate a high level of quality. However, all original research falls into this classification, and original research may be required for many assignments. Examples: clinical trials, case reports, research reports.
Secondary sources aim to review or summarize several to many primary resources. Some of these, such as well constructed systematic reviews, have tremendous value. There is more focus on interpretation. Examples include: reviews, guidelines, and books.
Secondary sources are often the first places to look for information to provide background on a topic. Library owned or subscribed resources have been carefully chosen and are usually of reasonable quality. However, it is important to keep in mind that because these types of sources are based on an author's perspective/summary, they are not always objective sources of information and need to be evaluated for bias.
It is easy to locate much more information using free web resources than necessary, and quality is variable. It is a good habit to use web resources to get a sense of a topic, but they need to be carefully evaluated before referencing.
Using advanced features in search engines is one strategy to improve the quality of results retrieved. For example, try date limit, restrict to domain type, such as .gov or .edu, or limit where your words appear on the page. View seach help in Google or other search engines to get more ideas.