Besides the obvious expansion of lessons, there are many ways for you to contribute, even as a beginning student of Cantonese. Some are listed below. Add your thoughts as to what you think should be done to the Planning page so that discussion is not lost, scattered throughout various discussion pages.
Other Ways to Contribute
Stroke Order Images
There is a project on Wikicommons to upload images and animations of the stroke order for characters. There are directions on how to contribute. It's easy with the use of some free programs and can be done even with only a basic understanding of stroke order. Please contribute so that we'll have a standardized reference for this and other Wikibook users.
With a microphone and a read through the recording guidelines for the Spoken Wikipedia you can contribute audio examples. Sound samples are particularly important for beginners, especially ones who are studying alone with no teacher or native speaker on hand.
You can see what has been uploaded so far at Category:Chinese pronunciation.
Currently, the English version is the most developed of the Cantonese Wikibooks. If you know another language, please check if a Chinese book is started in that language and compare it to this one. You can make changes to their content based on ideas gained here, or do a wholesale translation of this textbook into the target language. Since the Cantonese parts can stay the same across languages, a lot of lesson development work can be saved in this way.
If you can only do a partial translation, leave a note to later contributors linking back to your source (a good candidate for using Templates).
Add InterWiki Links
If you can't translate pages, but know enough of a language to locate the corresponding Cantonese Wikibook, you can make Interwiki links. You can see them on the Wikibooks Sidebar listed under "in other languages" when available. They are typically placed at the very end of a page using a simple format. Here is the list used for the Cantonese TOC page:
In addition to the main page, Lesson pages, Stroke Order pages and anything else can be interwikied as long as the content is the same.