Roll off, or de-emphasize, the frequencies below 100 Hz if the guitar tone has unwanted low-end rumble.
Boost the equalizer between 80 and 200 Hz and between 600 and 800 Hz if you want to add thickness to the jazz guitar tone. Most jazz guitar tones will have ample thickness in these frequency ranges. Because of this, usually only a small boost is needed in these regions. If the guitar tone sounds too thick, cut the equalizer in these frequency ranges.
Boost the equalizer between 800 Hz and 1 KHz if you want to add definition to a jazz guitar tone that is too dark. Cut the equalizer in this range to darken a guitar tone that has too much definition.
Boost between 2 and 3.5 KHz if you prefer a slightly brighter jazz guitar tone. Cut in this range if you prefer a darker jazz guitar tone.
Boost between 3.5 and 5 KHz and between 5 and 8 KHz to add "sparkle" to the jazz guitar tone. Some jazz guitarists like this addition, others do not. If you notice the guitar becoming thin by boosting this range, this is a sign that you have boosted these frequencies too much.
Boost between 8 and 12 KHz if you prefer a bright jazz guitar tone. Do not boost in this area if you prefer a darker jazz guitar tone. If you notice that this range adds noise when boosted, cut the equalizer in this frequency range instead.