The basics are that a font should have immediately recognizable characters (aka glyphs), so that you could read text on a road sign or an indoor navigation sign

The basics are that a font should have immediately recognizable characters (aka glyphs), so that you could read text on a road sign or an indoor navigation sign from afar, in bad lighting, while moving and being nearsignted (it's sorta an edge case but a good one). At the same time, glyphs must form a line that guides the eye without making it stumble—there should be no jarring inconsistencies, of which wrong letter-spacing is a case. Glyph shapes affect the perceived spacing, so there's interplay between the aspects of a font. The Kern Game is a good primer: https://type.method.ac/ https://type.method.ac/ As usual, learning to see good fonts is a matter of recognizing bad ones first. You'd want to look at reviews of bad fonts, more-or-less detailed. Then there's also the matter of the font style: a decorative font may easily have an untasteful twang to it (e.g. “playful” ad fonts), or be overly pretentious for the task. This is also a matter of looking at a lot of examples and thinking of what they make you feel. These are just the basics, and designers sometimes diss fonts that look fine to me. But these help. Also, IMO learning to see and apply the proximity principle covers a lot of design, including typography (e.g. line spacing and paragraph positioning).