Let's begin with eyes, draw two ovals close to each other, then pupils, a nose in the form of carrot and widely opened mouth.

Further we draw a shape of the head, a foretooth, eyebrows and three filaments in the form of sticks.

Draw Olaf's body, then feet, three cambers and hands.

Can also draw a flower, darken at Olaf an oral cavity, hands and something like buttons (these convex krugleshka).

Look Elza and Anna from this animated film.