They say all other senses become heightened when you lose sight. Thus, what better way to familiarise ourselves with minor and major 2nds than by closing our eyes.
Start by choosing a random note. Continue by playing the next fret up – the relationship between these two notes is called the minor 2nd. Do this until the aural characteristics become ingrained in your mind. In a matter of minutes you will be hearing the second note in your head before you’ve even struck it.
Once comfortable, challenge yourself by selecting a note at random and trying to find its minor 2nd on the string below; if you start with F on the A-string, try to locate it’s minor 2nd on the D-string.
Generally (note emphasis), if you miss the minor 2nd, you’ll land on the major 2nd (on a single string, the major 2nd is two frets up from the starting point). Through trail and error, you will soon be able to discern between the two variations.
It seems everyone has their own way of distinguishing the two. To me, the minor 2nd sounds eery, the major 2nd bright. Everyone interprets sounds differently so the best way to get around them is to develop your own way of seeing in the dark.