According to the IOM [1], clinical practice guidelines are "systematically developed statements to assist practitioner and patient decisions about appropriate health care for specific clinical circumstances."
The best guidelines will be evidence-based which means that they are developed by performing a systematic review or meta-analysis of the available evidence from high-quality clinical trials and research studies which is then synthesized by those with expert knowledge into recommendations.[2]
Clinical practice guidelines can be found in books, websites, and databases. Some professional organizations have their guidelines freely available and other only allow members access to them. Many organizations publish articles on their guidelines which is why they can be found in academic databases like PubMed.