I agree with darcshadow about the blade depth. Do not use any instructions that have to do with using a credit card or post it notes. They are wrong.
To start with, you should set your blade depth correctly, by taking the blade holder out of the machine, and firmly cut across a piece of scrap vinyl, you will be cutting. You should only be cutting the vinyl and barely a mark on wax paper backing, Adjust blade to get there, Then put the blade holder back in machine, and use the force of the machine to get there, same results, only cutting the vinyl and barely a mark in wax paper backing. You should barely see and feel the blade out of the blade holder. Regular sign vinyl is only 2-3 mil thick. You only cut with the very tip of the blade.