The right headphone settings depend entirely on your specific pair's natural tuning, which varies a lot between brands and price points.
Play a familiar, well-recorded track and listen for what's off: too much bass suggests cutting 60Hz, recessed vocals suggest boosting 500Hz–2.5kHz, harsh treble suggests cutting 8kHz. Match the adjustment to what you actually hear rather than a generic preset.
Settings tuned for one headphone rarely transfer well to another — if you switch to a different pair, start again from Flat rather than assuming your previous headphone settings will still be correct.