Reading the Track
Now that you understand the basic mouth positions, it's time to break down the track. If you have animator's exposure sheet paper, use it. Otherwise, get a pad of lined paper on which to write your track, using one line per frame. (If you prefer, you can create a spreadsheet for this purpose and do it all digitally.) Load the dialogue into a sound-editing program.
Match your sound-editing program's timebase to the timebase that you're animating30, 25, or 24 frames per second, for example. After your timebase is set, selecting a snippet of dialogue should enable you to listen to the snippet and read its exact length on the editor's data window. The visual readout of the dialogue gives you clues as to where the words start and stop. Work your way through the track and write down each phoneme as it occurs on your exposure sheet, frame by frame.
Some packages give you the capability to play back audio in sync with the animation. This feature is particularly helpful because you may be able to skip the step of reading the track and simply eyeball the sync. However, this will not be as accurate as a frame-by-frame read.