You can generally put a spider web anywhere in your crazy quilt. In the past it was felt that spider webs in a crazy quilt brought good luck. What I like about putting a spider web in my quilt is that spiders and their webs are part of the natural world like the bees and the butterflies and the flowers. I try to include one web in every quilt, maybe even two.
Then come up on the left side and travel to the following spoke. Repeat this until you have gone all the way around. When you come back to your starting point go down on the left side of the spoke. By coming up on the left and down on the right you will lock your spokes into place. This will begin to create the structure of your web. Repeat this with several different level coming out from the center of the web.