Step 1: Take your glassware and score it along whatever areas you want to create whatever kind of shapes you want.
Step 2: Prepare a bucket with extremely cold water and ice in it for the bottle to be dropped into.
Step 3: Heat up the bottle along the areas were you scored it using a lighter.
Step 4: Drop the glassware into the bucket of cold water and the areas were you scored the glassware should separate from the rest of the glassware.
Step 5: Decorate using those glass pieces however you see fit.
Note: You probably want to be scored into the glass fairly far, have very cold water, and have it heated up very high.