Some people have learned to cut glass as part of the introductory glass or glass fusing class or workshop. The others just learn very basic skills in the mode of trial-and-error, or with a friend to give them some pointers, and maybe (if you're lucky) demonstration.
Though there are several fusing supplies available, you have to use them carefully, especially, cutting glass supplies. There are some things one should never do when cutting art glass. Let's take a look at them:
Avoid pressing too hard when you make a score in the glass. You'll know you're pressing too hard because the scoreline will be highly visible "early" and you can even see tiny shards of glass to fly away from the scoreline as you move your cutter wheel across the surface of the glass.
Also, avoid pressing too lightly when making a score. It will become clear in a few ways. You will not be able to hear the score is made and/or the scoreline will be very faint, if visible at all.
NEVER re-score through the channel you've scored already. This is a definite no-no! When you do this, you not only ruin your cutter very quickly if you do it repeatedly, but you also run the risk of your glass does not violate either.
Do not run your glass cutter directly from the edge of the glass and make it go away "noise" as your cutter hits the table. This may sound attractive, but also shorten the life of your cutter, and it's really not necessary.