VisionLib's SDK for Unity is the easiest way to get started, because you can quickly setup tracking with VisionLib and use the Unity engine for rendering and application logic.
We've prepared step-by-step tutorials on how to use VisionLib with Unity. To get started, we recommend the quick-start:
Besides, we offer tutorials showing how to use VisionLib's tracking techniques from scratch:
The illusion of augmented reality relies on the effect of precisely superimposed visuals within the augmented views. That said, camera calibration and getting core tracking parameters right is essential. For this, we recommend also looking into tracking essentials:
Update: For more trouble shooting, have a look at the FAQ section.