Working in a spiral is one of my favorite ways to work for a flat circle, amigurumi or likewise. The reason is, you don't get ugly looking joints, as if you close each round with a slip stitch. And yes! I do know there are prettier methods for seamless joining than the slip stitch.
If you want to read more about seamless joining, then Kathryn Senior got a really good description in http://www.craftsy.com/ with the article 6 Hacks to crochet a Circle That Actually Lies Flat. And there are other good ideas out there, BUT if I can get away with it, I prefer the spiral technique :)

How To Work in a Spiral

It is really simple. Everyone can do it. You simply crochet round and round and round. All in the same direction. No extra or special stitches. The hard thing is to keep track of how far in the current round you are - or worse - how many rounds you've actually done. And believe me. I've tried counting and counting, when I lost track. And once you are lost, it can be almost impossible to figure out what you've done.



SO! I use a little string as a marker. I tried those little plastic marker things you can buy, but in a tight crochet work they make holes in my project, making it look less regular. A cotton string is much better. Cotton doesn't get entangled with your work. And I prefer the string to be at least 30 cm long (12 inch).

Before I start a new round, I put the string in between the hook and my loose end of yarn.




When I get to the string, I know, I've finished that round. Then I put the end of the string between my hook and the loose end of yarn. Some pull it out first and then replace it. I don't. I let the yarn end stay. The one that is already weaved in once.



TADAAA!