There aren't many books about marbling, and even if I could get my hands on them, many are out of print. Furthermore, paging through a book of color images and samples of marbled papers only provides you with the end result, and not the process of HOW to actually make the patterns.
My best bet is to keep experimenting with paint and trying new things. Sharing ideas with other marbling "nerds" helps, too. I signed up for an online marbling workshop with its own private Facebook group where me and my fellow marblers can post our images and ask questions. The instructor checks in on scheduled days/times and helps us troubleshoot any problems we might be having. She also provides professional videos, shot from above the marbling tray, so that we can observe each drop of paint as it falls into the tray.
Thanks to this new avenue of learning and sharing, I am getting the courage to loosen up and break rules with my marbled patterns! I hope this shot of courage (as I ask myself "what if?") leads me to paint more innovative and interesting paintings in the coming year.