Step one:

The main tool were going to focus on this tutorial is the Pen tool. You can draw Stewie in different angle, experessions etc so when you try this tutorial, experiement with different shapes for different parts. Start with a #FEFBB8 background canvas. Create a new layer-set called Sticker, add a new layer and draw the head with this color code #ECD4B0. Add a Stroke layer style.

Step two:

In a new layer, draw the left eye using ellipse tool, Same color code as the head. Add a Stroke layer style.

Step three:

Now add the right eye, same step as the last one.

Step four:

His eyes are going to be half open so draw white shape inside the circles. Add a Stroke layer style.

Step five:

Finish the eyes with two dots.

Step six:

Take a #000000, 1px hard brush and draw the hair and eyebrows.

Step seven:

Again with the 1 px brush, draw the nose.

Step eight:

Back with the Pen tool, create the mouth.

Step nine:

Add more details to the mouth by adding 1px lines on the upper and bottom side of the mouth.

Step ten:

Merge the layer-set and add Drop Shadow, Outer Glow, Gradient Overlay, and Stroke layer styles