Revit 2013 provide the online Revit Developer Guide. It is a good resource to get started and deep into Revit programming.
We provided the "My First Revit Plug-in" instruction for those who don't have any Revit programming skills.
In addition to that, ADN recorded the DevTV to get started with Revit programming. You can find them in this page.
Hope this helps.
Developer Technical Services
Autodesk Developer Network