Connect a parametric equalizer to your mixer according to the manufacturer’s instructions. Assign a center frequency and frequency range to the vocal track. The center frequency is the frequency of the human voice that sounds clearest and most melodic to the human ear. Typically the frequency range for the human voice is 300Hz to 3000Hz, or the standard bandwidth of a telephone line. Choose a range within the 300Hz to 3000Hz range and dedicate it exclusively to vocals.
Set a high-pass filter on the parametric equalizer to cut off all sound below the chosen vocal frequency range.
Set a low-pass filter to cut off all sound above the chosen vocal frequency range.
Decide on the exact frequency mid-point for the vocals and amplify, or boost, that frequency to make it louder and give it prominence, taking care not to overdo it. Less is more where boosting frequency is concerned.
Mix in the rest of the instruments in the same way as the vocals, taking care to give each its own frequency range so that no instruments overlap each other or the vocals. Fine-tune as needed during the final, master mix.