Almost every sound has frequencies that sound nice, and frequencies that sound bad. The goal of cutting frequencies is to find the bad-sounding frequencies and reduce them, so there is more space for the nicer frequencies, and also more space in the mix in general.
You can find the bad-sounding frequencies by doing an EQ sweep. To do an EQ sweep, take one band in the EQ and boost it up quite high, and make it narrow. Then play the sound, and move this narrow band across the frequency spectrum. Overall this boost may not sound nice, but at some frequencies it may sound extra bad, and that is where you want to make a cut. To make the cut, get a band at the frequency you found, and turn down the gain until you feel you’ve taken out enough. If you take out too much, the rest of the sound may start to sound hollow or thin. Usually, cuts with a narrow band are better, because you will take out the problem frequencies, without affecting too much of the rest of the frequencies. A sound may need zero, one, two, or more cuts, depending on the sound. Use your ears to find the frequencies that need a cut.
Song used: Dread Pitt & Yung Fusion - The Mission