How to Stuff and Shape Amigurumi
Good stuffing can make or break an amigurumi project. Too little and your piece will look floppy and sad. Too much and the stuffing will poke through the stitches. The goal is a firm, smooth shape with no lumps.
Polyester fiberfill is the most common stuffing material. It's lightweight, washable, and easy to work with. You can find it at any craft store.
Preparing the stuffing
Before putting stuffing into your piece, pull it apart into small, fluffy tufts. This prevents lumps and gives you much more control over the shape.

Stuffing technique
Add stuffing a little at a time. Push it gently into the piece, focusing on the bottom and edges first, then filling the center. Use the eraser end of a pencil or a chopstick to push stuffing into small pieces like arms and legs.

Keep adding small amounts until the piece feels firm but still has a little give when you squeeze it. You should not be able to see the stuffing through the stitches.

For pieces worked in the round (like heads and bodies), add stuffing as you go rather than trying to stuff everything at the end. It's much easier to get an even fill this way.
Tip: If your stitches are too loose and stuffing shows through, try going down a hook size. For amigurumi, you generally want a tighter gauge than the yarn label suggests.