Once you have created a great "static mix" you may now wish to automate the vocal in order to make them sit perfectly in the mix. This will create a smooth dynamic for the vocals that reside.
With the track assigned to the corresponding on your control surface, switch to the Edit window in Protools.
Scroll to the intended vocal track and zoom out vertically to expand the track for easier viewing.
You may also wish to change the track display to "Volume." This way you can see the actual automation moves you are making.
Play the song within a couple of bars that precede the start of the vocal and prepare to begin "riding" the fader. I like to mute the background vocal when riding the lead vocal. In most cases, the background vocals are not in a comfortable place and can confuse your lead vocal.
Vocal riding is a purely visceral and intuitive process and is specific only to the song at hand-so start by finding a starting level, which you've probably already established, and start riding the fader until the vocal feels like it's right "in the pocket."
Once you've completed these rides you can continue with the background vocals. In most cases you will want to use them to enhance the lead and not upstage it. With the lead vocal in place you now have a frame of reference.