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.