start by drawing the outline of the top part of the upper lip.(tap picture for better view)
add the bottom line of the upper lip; just follow the curves of the upper line.
draw the top of the bottom lip. connect the bottom of the upper and the top of the bottom lip and extend the line a little.
draw the bottom part of the lip, which is like half of an oval.
add teeth by drawing rounded corner squares. add details.
there you go! :) i'll add a guide to color this soon