Here, I found very useful tutorial on youtube on how to start adjustable ring for crochet amigurumi.When I start to crochet amigurumi doll I always start this way.
This is how I did on single crochet increase by LionBrandYarn.
Here another one of crochet increase by staceytrock at freshstitches.
Invisible crochet decrease.
This one by nerdigurumi.
And another one by roxycraft.
Thank you for watching. I hope this tutorial will help you to start and get into amigurumi(crochet stuffed animal that make you addicted).