The physical size of the screen of mobile devices is smaller
than on the desktop, although their pixel density is higher. Sharper
text is nice to look at, but the glyphs have to have a minimal physical
size to be legible.
Mobile devices are often used on the move and under poor lighting
conditions. Consider how much information you can realistically
display onscreen legibly. It might be less than you would display
on a screen of the same pixel dimensions on a desktop.
Use typographic hierarchy to highlight important information.
Use font size, weight, placement, and spacing to express the relative
importance of the elements of the user interface. You can use one
or more cues at each level of the hierarchy. Apply these cues consistently
across your application. A cue can be spatial (indent, line spacing,
placement) or graphic (size, style, color of typeface). Applying
redundant cues can be an effective way to make sure that the hierarchy is
expressed clearly. However, try using no more than three cues for
each level of grouping.
Try to simplify the labels and explanatory text required. For
example, use sample input in text field to suggest the content and
avoid a separate label.