With the launch of Office 365, which includes Exchange Online, Lync Online and SharePoint Online, there are a number of great resources available for developers to help get you started developing on the platform.
First, for Office client-related development, there is a short white paper Guidance for Office Development in Office 365 that calls out a few of the key things to have top-of-mind relating to the Office clients and O365 SharePoint Online (SPO). The most significant callout is managing remote authentication in your Office client add-ins. Since O365 SharePoint Online is not in your Active Directory domain, you need to be able to pop the credential prompt for O365 when you need to access data in your add-in for the end-user. This white paper points you to a code sample you can use with the SharePoint Client Object Model and talks you through the pattern for how to implement it in your add-in. Additionally, you should keep a copy of the SharePoint Online Developer Guide handy to use as a reference for all things related to basic SPO development. Or you can access it online as well.
Secondly, my colleague Chris Mayo, has a blog post describing the Office 365 Developer Training Course on MSDN and downloadable training kit that have been released to correspond with the launch. I won’t replicate his blog here so be sure to visit it to see the training course modules enumerated and described and other great resources.
Some videos available on Channel9 you might want to watch for O365 information are: