You should begin mixing your vocal tracks after you have a basic balance of the backing rhythm tracks which will help define the overall style of the song. Begin by compiling the best vocal takes from each section of the song into one main vocal track. To do this, listen carefully to each take of each section and decide which take best captures the emotion and feeling of the song. Copy the chosen sections from the selected takes and paste them in place on a new mono audio track which you might name "Vocal Comp." Create proper cross fades between takes by highlighting the end of one region and the beginning of the next region and hitting the "F" key. If needed, judiciously use vocal tuning software to correct off-pitch notes or as a special effect.
Listen carefully to the vocal and decide which processors will enhance the vocal track. Often times compression can be used to tame the dynamics of a vocal and also add a distinct character to the sound. Depending on the type of music your compression settings will vary. Rock music typically uses more compression while softer genres use less. You can start with a 4:1 ratio, medium attack and fast release to achieve 6dB of gain reduction on loud sections and make changes from there. Use the make-up gain feature to compensate for the compressor's reduction.
Equalize the vocal to remove harsh frequencies and boost pleasant frequencies in the voice. Use a parametric or graphic equalizer and boost a frequency by an exaggerated amount to hear it in more detail. Slightly cut frequencies that do not enhance the voice. To remove low-frequency rumble, consider using a high-pass filter on the vocal at around 80Hz. To enhance the "air" and upper frequencies, consider boosting a high-shelf around 8kHz. You might need to add a de-esser plug-in set to only compress the harsh frequencies of the "ess" sounds.
Depending on the type of music that you are mixing, you most likely will need to add in spatial effects to the vocal such as reverb and delay to enhance the vocal or to make it sound more natural. To do this, create a new stereo auxiliary track for each effect that you will be adding. Set the track input to any unused stereo bus and the output to your main output. Create a send from your main vocal track to the auxiliary track using the same bus and set the level accordingly. Insert a spatial effect plug-in on your auxiliary track such as a nice reverb or delay. Be sure to name the track accordingly. Sends from your vocal track are automatically post-fader, meaning the send level is based on the relative level of the track. It is best to leave it this way. When you have completed all of the automation, change the automation mode to "Read."
Automating the vocal track is a very important part of the vocal mixing process as it creates a flowing, more dynamic vocal which can bring power and emotion to a track. To do this, set the vocal at a level which sounds right. You should be able to clearly understand the lyrics while not being over powered by the vocal. Set the vocal track to an automation mode that you desire to work in such as "Latch" or "Touch." Play the song from beginning to end while "riding" the vocal fader using your mouse or an external controller. You might need to record the automation multiple times as you learn repetition. You can always go back and manually draw automation using the pencil tool as well. You may also automate your vocal sends to create varying and dynamic spatial effects.