Read reviews/critiques of mobile apps by medical practitioners and researchers. iMedicalapps.com publishes reviews of new mobile apps and other technologies by medical professionals. Many journals also publish reviews/critiques of mobile apps.
Consult websites or conference proceedings of a recognized professional association or regulating body in your field to determine what mobile apps are being used in or recommended for your field.
Look into who created and who helped develop the app. Thinking about bias, it can be helpful to know if any MDs or other health/medical professional were involved in the app's creation, as well as funding sources (organizations, corporate entities, etc).
Is the information contained in the app referenced (cited references to the literature)? Is the app evidence-based (if applicable)?
For a deeper dive, check Xcertia mHealth App Guidelines [accessed January 7, 2020] which cover privacy, security, content, usability, and operability.
This link will take you to the NHS technical and safety criteria - helpful for evaluating digital health technologies. The National Health Service (U.K.) has retired their library link. Apps will be listed throughout the NHS website.
Medical App Libraries
Here are some links to libraries for evidence-based and validated medical apps.
Select the "App" filter to limit resources to apps and click the "submit" button to run the search. Retrieves a listing of freely available resources by the U.S. National Library of Medicine optimized for mobile devices. Includes resources such as AIDSinfo Drug Database and PubMed® for Handhelds.