Guidelines (also known as clinical practice guidelines, practice guidelines, and CPG's) are high-level evidence because a group of experts has reviewed the existing evidence on a topic, graded the evidence, and made recommendations for how to implement the evidence in a clinical setting. Guidelines can be developed on the international, national, state, and local level by health organizations, hospitals, and other groups, but always check the quality and authorship to be sure it is trustworthy and can be used in patient care.
You can find guidelines by searching for part of your topic (usually a specific disease, condition, or intervention) through the sources below.
From "Clinical Practice Guidelines We Can Trust" (2011)
Institute of Medicine (US) Committee on Standards for Developing Trustworthy Clinical Practice Guidelines; Graham R, Mancher M, Miller Wolman D, et al., editors. Clinical Practice Guidelines We Can Trust. Washington (DC): National Academies Press (US); 2011. doi: 10.17226/13058