Assemble all the parts of the character on the stage, except for the mouth, and lock the layer.
Insert a new layer above the first and drag the mouth into place.
Import the dialogue clip into the Library.
Insert a new layer above the previous two.
Drag the sound clip from the Library onto the stage in the new layer.
Extend the time line to the length of the sound clip. The frames in the sound clip's layer visually display the wave form of the sound, allowing you to see the parts of the clip.
Click on the sound's layer in the list to select all of the frames, and open the property window.
Set the sound clip's Sync property to "Stream." This will allow you to hear the sound as you scrub the timeline.
Press "Enter" to play the timeline, or scrub the timeline to find the first syllable of the dialogue.
Insert a new key frame one frame ahead of the first syllable. Doing this helps to better align what the viewer sees with what they hear.
Swap the current mouth symbol with the one appropriate for the syllable.
Play or scrub the timeline to determine the next sound or syllable, and insert a new key frame at that location.
Swap the previous mouth symbol with the next appropriate symbol.
Continue this process to the end of the sound clip.