I'm going to attempt cutting a big mirror. Does anybody have any tips/tricks that might help?

Thanks

 

Don't break it.

 

Score more times than you think you need. Uses a heeavy straight edge to guide the score. tape the edges of the score line, to keep the crack from running. Lay a thin dowel under the "Keep" side at the edge.
Geet a glass cutter to do it.

 

I have never tried it, but watching one of those "How its made" shows they were cutting glass on an industrial scale. they scored and used a torch to break it.