Set up your mixing environment so that the vocal track will play alone. Usually, this is done by pressing the "solo" button on the vocal track's channel strip, or by pressing the "mute" button on all other tracks.
Insert a multi-band EQ on the vocal track's channel strip. This procedure will vary depending on your mixing environment, but all mixing environments -- hardware and software -- have channel strips associated with each track. The channel strip will at a minimum contain a volume slider, a panning knob, insert slots and send outputs. Insert the EQ on an empty insert slot. If there are other devices such as effects already inserted, insert the EQ at the earliest point possible in the signal chain and bypass other devices.
Zero all the EQ sliders. The EQ will have several sliders corresponding to different sections of the overall frequency range the human ear can perceive. This range runs from about 30Hz to 18,000kHz. The number of sliders on the EQ will vary. Generally, the more sliders there are, the more precisely the tone can be adjusted.
Play back the vocal track. The dominant frequency range of the human singing voice runs from about 200Hz to 1,000Hz, and it is within this range that the fine adjustment will take place. Listen carefully to the vocal track. Is it too bright? Muddy? Dull? Can you make out each word, or are the consonant sounds muted? Good tone is largely a matter of preference. Play the vocal track through once without adjusting EQ to clearly identify any tonal problems.
Cut all sound information below about 75Hz. Frequencies below this range only serve to muddy the overall mix. Doing this helps to clarify the vocals. Move all frequency sliders associated with this range on the EQ to the bottom.
Increase frequencies between about 200 and 1,000Hz to make the vocal tone brighter. Decrease these frequencies to flatten the tone. Usually, increasing this range even slightly gives both male and female vocals greater presence. With vocals that are too rich, too loud or too present, decreasing frequencies within this range will reduce the problem.
Increase frequencies between about 2 and 5kHz to emphasize consonant sounds. This will help a vocal track in which individual words are difficult to make out become clearer. If consonant sounds are overemphasized, decrease EQ sliders within this range. Sometimes, particularly with male vocals, cutting all frequencies above about 15kHz will help to reduce any hissing "s" sounds present in the recording.
Experiment with different EQ settings until you find a vocal tone you like. Each voice is unique and will need different EQ settings. Remember that you are not changing the frequencies themselves, but the relationship between the frequencies inherent to that sound. Once you find the right tone, un-mute all tracks, re-engage any effects inserted on the vocals channel strip. Press "Play". Repeat steps six and seven to make any fine adjustments to vocal tone relative to the backing tracks.