I am now convinced, for unexperienced users this might be the only chance to get them understand and use all the features. So here are some ideas for tips:
You want to start from 0? This could be a helpful first tip (to prevent the question: Where has coccinella gone:).
You can click on the coccinella besides the clock in the taskbar to make the contacts list disappear/reappear. If you close coccinella by clicking the X it will be hidden...
But I would include this tip in a elaborate how-to for new users describing in short how/where to get a jabber account and in detail how to make coccinella use this account, how to add first buddies.
How to add buddy icon (valid sizes, formats)
If exists (I still don't know): How to change preferences only available per config-files.
What the whiteboard is for and how cool it is :)
Introduce chatrooms as a possibility to talk to many users at the same time.
What a transport is and what the profits are.
Perhaps what you can learn from the "services" tab.