It totally depends on your playing style and the amp you use. It's always best to experiment with differing pickup heights while playing at gig volume.
A good general starting point is about 3/32" from the strings when they're pressed to the last fret.
A simple way to achieve this is to lay the guitar flat, face up. Place a US nickel atop the low E side of the pickup and lightly hold the low E string to the last fret. Adjust the height of the low E side of the pickup so the nickel is just barely in contact with the string. Do the same with the high E side, and then do the other pickup(s) the same way.
This is not the optimum height; it's your starting position, and you adjust in quarter turns up or down and see how it affects the responsiveness of the pickups.
Players that pick with a light touch generally like the pickups on the high side. Those with a heavy handed style usually prefer pickups farther away from the strings. Note that a small adjustment can make a big difference, depending on the sensitivity of your amp.
Bill Lawrence suggested one nickel for the high E and TWO nickels for the low E, never read the nickel method as same height both sides?
IME that delivers a louder low E and a less loud high E.
Also tends to overdrive the low end of the amp more than I prefer, lower under the low E delivers clearer less muddy bass, and I hear a fatter high E.
But of course we all have a target sound and many players like the bottom dirty & crunchy.
Here’s an Esquire with my usual setup, old rewound Fender pickup around 6.8-7k or so.
