Opening champagne with a sword or saber may seem like an impossible task, or a trick from a magic show. In reality, it is much easier for the average man or woman to do. All it takes is the right tool (this champagne saber to start, a bit of practice, and a bit of knowledge.
First, prepare by having the WHOLE bottle chilled. This means leaving it in a fridge until it is around 35 degrees Fahrenheit. It is important that it is chilled in a fridge rather than an ice bucket. While the ice bucket typically used for cooling, this method only cools the lower part of the bottle.
For sabrage, the entire bottle (including the neck) needs to be chilled. This helps make the glass more brittle, and makes it easier for a clean break. When removed, it needs the wire and foil around the cork removed. Once chilled, hold the glass at about a 30 degree angle facing away from the body. Find the seam of the glass bottle. Run the blunt side of the knife quickly away from your body, making impact at where the seam hits the lip of the bottle.
If done correctly, this should send the cork flying, with glass around it in a clean break. There are numerous videos online available should you still struggle.