Here's a video from Dick Blick showing for sharpening pencils
YouTube - Blick Presents: How to Properly Sharpen Prismacolor Pencils
This is an article to help with broken pencils and tells you how to "fix" them.
Quick Tip For Prismacolor Pencils | Industrial Design Sketching and Drawing Tutorials
Thread on SCS about broken pencils, sharpening etc. - Scroll down on the page to get to the info you want.