I’m sure that clipping paths and opacity masks in various graphics tools are nothing new to many of you, but they are something I continually screw up.  Thankfully, VectorTuts+ has a tutorial demonstrating their use.

Opacity Masks and Clipping Paths are two of the most used tools in my workflow. They allow me to easily reveal or hide artwork without deleting any paths. As in all digital arts, it’s best to design your workflow to allow for maximum editability. It is inevitable that either myself or the client will change their mind through the process and this technique allows for easy revisions and edits, leading to less stress and happier clients.

The Basics of Clipping Paths and Opacity Masks – Vectortuts+.