Watch a video of people talking. This will not only help you observe the character's features as he's speaking, but it will also help you gauge proper camera positions and lighting for your 3-D animation. Also watch people talk in your everyday life. Take notes about their gestures and facial muscles, and how they physically react to various subjects. Note everything from eyebrow movement and blinking to the way their face turns and speech patterns.
Complete the character's voice-over with a sound or voice recording device on your computer. Most computers come with a default recorder, such as the program "Sound Recorder" but if yours does not, you will have to buy or download one. Record your voice by clicking any button that resembles a red circle or that says "Start Recording". Using your desktop microphone, record your voice and click "Stop Recording" when you are finished. Save the file as an audio file.
Open your animated file. Look in the mirror and slowly repeat the words that the character will be saying and use this to manipulate the character's face to match your own. Take care to accurately express your character's every movement, including the cheeks, forehead and arm gestures. Facial expression will often be conveyed through the muscles around the eyes, eyebrows and eyelids. For example, if your character is sleepy, allow the eyelids to be half-closed. Muscles around the mouth will also help display emotion, such as raising the cheeks slightly to show a smile.
Repeat Step 3 in every frame (or every few frames if the program you're using will seamlessly blend each frame) until you have finished the sentence. Remember to manipulate the character's chest so it appears to be breathing in before he speaks. Also make sure the character blinks occasionally, and move the eyeballs so he does not have a blank stare. Save the file.
Upload the sound and video file into a movie editing program by clicking "File Import" on the "File" menu; select the files one at a time. You may have to drag the files onto the timeline into their respective places, with videos on the "Video" line and audio on the "Audio" line. A movie clapper and a speaker icon usually represent video and audio, respectively. Maniuplate the audio file by deleting or stretching segments until it appears to sync with the video. Save your work.