from SOUND ON SOUND
• If your mix sounds 'muddy', boost the main frequency range of each of the principal instruments. Boost 'decorative' sounds even more and pull the faders right down.
• If you can't get your tracks to blend together in the mix, cut the main frequency range of the principal instruments.
• To make vocals stand out in the mix, boost at around 3kHz.
• For extra clarity, cut the bass element of instruments which are not meant to be bass instruments.
• Adding EQ boost often adds noise. Listen carefully to arrive at the best compromise.
• Changing the EQ changes the level. Always consider re-adjusting the level after you EQ.
• If you add a lot of EQ boost, you may run into clipping and distortion. Reduce the channel's gain to eliminate this.
• If you use EQ to reduce feedback in live work, take care not to take too much level out over too wide a range of important frequencies, particularly the vocal 'presence' range around 3kHz.
• If your mixing console has an EQ Off button, use it frequently to check that you really are improving the sound.