I found some really cool ideas from these places listed below:
http://frubilledkunst.blogspot.nl/2012/06/op-art-4del-hvidlgsfed.html?m=1

 
Great visual instructions from Fru Billedkunst Blog

http://beckermiddleart.blogspot.com/2015/01/falling-into-op-art.html

Love this example from Becker Middle School

http://kidsartists.blogspot.com/2010/06/op-art-line-design-2-garlic-cloves.html
This was a great flyer to use with my students from Kids Artists Blog….Thank you for posting!
I gave my art club the flyers. They took a gander and started to create. These are pretty spiffiy and I love all the colors.
This Op Art Tutorial is AWESOME!
Check it out, 1969