Taking ikebana lessons usually also means taking photos of the arrangements, and sometimes drawing the finished results. This will help you see the development in your work over time. When you are drawing the arrangements you also learn to pay the attention to details, which is really important in ikebana.
There is a long tradition of collecting pictures and drawings of ikebana arrangements into books. In the Sogetsu school every student is expected to document his or her work in workbooks that are handed in when it's time for a new exam, a bit like a scrapbook or an ikebana diary.
I'm currently updating my workbooks with new ikebana arrangements. Some of the photos can be found on this blog. This process reminded me that I had planned to post a link to an interesting collection of ikebana drawings that is available on the internet. The library at the U.S. National Arboretum in Washington DC holds a collection of old ikebana books that were collected by Ellen Gordon Allen, founder of the organisation Ikebana International. On the website of the library you can download the book "Rikka shodoshu", published already in 1684 in Japan. The book title means "The right principles of rikka". It's a three-volume set of color woodblock illustrations. Each volume represents one of three styles of rikka arrangements known as shin, gyo, and so. They are also categorized by season. Volume one contains an introductory text in Japanese and English - so go ahead and explore the long traditions of documenting ikebana arrangements.