I tried to post a link of the pictures I followed to do this, but they have
been removed, so I'll try to explain as well as I can.
First set up a little table and cover it with anything that has a colored pattern, rainbow tissue, tie die shirt or make your own pattern. Next you will need a glass pan, pie plate, cake pan, loaf pan or something like that. Place the ends on books, glasses or anything that will raise it 6" or so (here's where you have to experiment) so that you have a clear view to the colored base. Add water, approx two thirds depth and drop in oil.
I used a macro lens shooting straight down. Manual focus was needed as the camera usually focused on the fabric, not the oil. You have to work fast as the oil drops tend to join together. When the oil drops join together, sir them up and start all over again.
Good luck, it was alot of fun.