Before inserting your hook in the next stitch, yarn over.
Now insert your hook into the stitch.
Yarn over again and pull through.
You now have 3 loops on your hook.
Yarn over and pull through 2 of the loops.
There should be 2 loops left on the hook.
Yarn over and draw through the remaining loops.
I haven’t seen many double crochets in amigurumi, every now and then I’ll use them to try and make a taller stitch, but it’s usually on a flat piece. It’s a good crochet stitch to know anyway, since you’ll often see it in other crochet projects – such as a beanie’s, blankets, etc.