There are a lot of guides out there, but I found this one especially helpful: https://productionadvice.co.uk/using-eq/.

Excerpted below for convenience. Lot more helpful info at the link.

50-60 Hz

• Thump in a kick drum
• Boom in a bassline
• Too much and you’ll have flapping speakers and a flabby mix
• Too little, and the mix will never have enough weight or depth

100-200 Hz

• This EQ band adds punch in a snare
• Gives richness or “bloom” to almost anything
• Too much makes things boomy or woolly
• Too little sounds thin and cold

200-500 Hz

• Crucial for warmth and weight in guitars, piano and vocals
• Too much makes things sound muddy or congested
• Too little makes them thin and weak

500-1000 Hz

• One of the trickiest areas
• Gives body and tone to many instruments
• Too much sounds hollow, nasal or honky
• Too little sounds thin and harsh

2 kHz

• Gives edge and bite to guitars and vocals
• Adds aggression and clarity
• Too much is painful!
• Too little will sound soft or muted

5-10 kHz

• Adds clarity, open-ness and life
• Important for the top end of drums, especially snare
• Too much sounds gritty or scratchy
• Too little will lack presence and energy

16 kHz

• Can add air, space or sparkle
• Almost too high to hear
• Too much will sound artificial, hyped or fizzy
• Too little will sound dull and stifled