Use the minimum size of a font that most people will be able to read.
Different displays have different brightness and pixel density. Combined with the user’s reading conditions, this can impact how they perceive the text.
Hierarchy
Any header should be emphasized in comparison to a text.
Emphasize the first level heading in comparison to the second level.
Font style
Try not to use too many font families and weights.
Use Regular, Medium, Semi-bold, and Bold fonts. Avoid using Ultralight, Thin, and Light, because they may be difficult to look at.
Contextual legibility
Test your fonts in different conditions. Users can work with your app in bright sunlight or at a distance. If you notice some difficulties, try changing the text or background color to improve contrast, and consider using different font sizes.