Here's a few simple steps that will guide you through the process of creating a digital sculpture that will then be 3D printed and painted.
Step 1: The Drawings
The first step is to start off with a few line drawings or illustrations of the character. From observing these drawings in a 3D application you will know how build and construct the digital form of the model.
Step 2: Sculpting Digitally
With the 3D application of your choice (I tend to stick with Maya and Zbrush) sculpt out the details of your character. Pay close attention to the contours of the face and the best ways to represent them in 3D space from the 2D representation of the line drawings/illustrations of the character to arrive at a sculpt that's true to the illustrations proportions and likeness. Once the sculpt is complete, seal off all holes in the model so that the model is air tight for the 3D printing process.
Step 3: The 3D Print
Once you have finished all of the digital sculpting, its time to send your model to a printing house. What you will get back from them is a model that looks something like this. On average there are a few errors that would need to be smoothed or sanded down to arrive at a nicely finished look.
Step 4: Painting the Sculpt
Once you have finished and worked out any slight perfections, you will want to pant the head. This is the final step in creating a toy.