A DJ mixer usually consists of bass, mids and treble knobs for each track. Practice using these knobs to control the tone of each song. Turning up the bass will add more low-end frequencies in your mix and will make your mix more booming. Turning up the mids will add more presence in your mix and allow certain frequencies to cut through easier. Turning up the treble will allow high-end frequencies to become louder. Depending on your song selection, adjust the bass, mids and treble accordingly so you have a balanced mix.
Boost the bass of one track and cut out the bass completely of another track so the mix does not become muddy and overly bassy. If too many frequencies have to compete against each other, the mix will sound overly busy.
Listen to your mix through your headphones to hear exactly how the two tracks you are mixing together sound before you play them for everyone to hear. You can adjust the equalizer settings accordingly to make a clean and balanced mix.
With practice, you will know the right amount of each frequency. Some tracks need more bass; compensate by turning up the bass knob.