Boosting at around 80-120Hz gives a low-end weight, such as in The Beatles' 'Yesterday', whereas the sound gets more of a boom to it a little higher at 200-300Hz, as in Nirvana's' 'Polly'. This latter song is also a good example of boost in the 2-5kHz range, which is good for clarity in rhythm guitars as it brings out the strumming. The 1-1.5kHz area, prominent in The Jam's 'That's Entertainment', can tend to sound a little nasal, while the 5-10kHz range emphasises the jangle or sparkle of steel-strung guitars in particular, Natalie Imbruglia's 'Torn' being a notable example.

Acoustic Guitar - EQ Fundemental

Boomy at 80 to 150 Hz.
Boxy at 150 to 300 Hz.
Hard at 800Hz to 1.5kHz.
Presence at 2.5 to 4 kHz.
Bright/scratchy at 4 to 8 kHz.
Airy above 8 kHz.