EQ plays a major part of sound. Whether you are mixing down a recording, or building your guitar sound, or anything else that pertains to music, EQ is one of the most important factors you have to deal with. Each instrument in a band has it's place in the EQ spectrum. The human ear can hear from 20 to 20,000 Hertz. Frequency is measured in Hertz. So, each instrument or vocal has a range of frequencies that it operates in. EQ can make a bass drum or bass guitar sound big and boomy to tight and thin. Or muddy and messy, if too much midrange is applied. Try to use common sense and good taste when mixing. Sometimes, less is more, or better. Instead of adding mids and highs, try taking out a little lows instead. Or vice versa. Experiment. What sounds best to you? What sounds best to you may not be what sounds best to everybody else. (You can't please everyone at the same time). But you can try to find a happy medium. Try to make it sound like stuff you hear on the radio or in a movie. Most of all, Have fun! Everyone has their own taste.