I've used an ancient (mid-70's) MXR 10-band graphic for years as the first step from a guitar to the next step -- either an FX pedal or chain, or straight to an amp -- but most often going direct to a recording desk. Most often, that last application is with a bass, or as a preamp with an acoustic guitar using a magnetic/passive soundhole pickup.
Markb's description of the curves to set the graphic at as 'smile' or 'frown' curves is about the best way to describe how to set it; the more bands the graphic has, the finer your control as you can cut or boost more selectively. Most pedals seem to be 6- or 7-band. (i.e.: Tom Scholz's set up in shaping his 'Boston' sound was an MXR 6-band as the first step from his LP Goldtop). Along those lines, I s'pose you could call it a 'sneer' or 'smirk' curve if boosting or cutting the lowest or highest ends of the spectrum, such as the lows and low-mids (with a DI'd bass).
With acoustic/electrics, Parametrics are the best bet as you can pick a particular 'notch' in the mids to cut or boost. Most of my a/e's have that type of onboard preamp. But I have an L.R. Baggs ParaAcoustic DI that I latched onto a few months ago, and it's so good I often bypass an onboard pre's EQ to use it instead. It also works great with a bass. I haven't tried it on my electrics.