Oliver Schöndorfer makes some points in his article How to pick a Typeface for User Interface and App Design?:
- Functional text: is short text. Labels, alerts, navigational elements, captions, and the like.
- Clarity: Make the Il1 test (capital I, lower case l, and the number one). If these three shapes are easy to distinguish you found a good typeface.
- Open shapes: The apertures should be open (like for c and e). Helvetica has closed apertures, while PT Sans has open apertures.
- Reduced contrast: Look for a typeface with even, sturdy strokes. This does not necessarily mean it has to be a sans-serif (some subtle slab serifs could work as well), but in most cases it might be.
- Set things legible: Letters set in all caps are harder to read.