First, there is no universal best setting. Equalizers (EQ) were designed to compensate in cases where deficiencies were introduced due to inefficient microphones. But these days, graphic equalizers are most often used to enhance your music.
How you wish to adjust your EQ depends on a bunch of things. The two key factors are the headphones you use to listen to music, and what type of music you are listening to.
If you have large, full cup headphones, they will generally sound more full and be able to produce a deep bass sound better than the little earbuds that go inside your ear canal, while those little ear buds may require you to turn down the higher frequencies.
My phone has 7 frequencies, 400 Hz - 650 Hz - 1000 HZ - 1500 Hz - 2200 Hz - 3500 Hz - 7000 Hz.
Generally speaking, with these settings, you could consider bass to be 400-1000 Hz. Treble, the high frequencies, would be in the 2200-7000 range. The middle, 650-2200 is midrange, you may notice there is some overlap. To get more "thump" in your low end, nudge the lowest bars, 400 and 650 up a little. Vocals generally sit around 2200 Hz, so giving that a slight boost will add clarity and presence to your vocals. If you are experiencing shrill, fatiguing highs, you'll want to lower the bar for 7000 Hz, and maybe pull 3500 down a little.
In the end, there is no right or wrong, as long as you think it sounds good! Experiment, or start with the presets and tweak the settings to get it just right for you.