Connie, there are some earlier posts on the g. about cutting glass by hand. It is a good skill to learn. There are times when something will come in that requires you to cut by hand - such as clock cases, cathedral door fronts, octagonal, oval, circle, fan shaped, and heart shaped frames. No reason to send this business elsewhere.
To add to Jim's suggestions, I have found that running the score by tapping on the back side of the glass (the side opposite the score) with the ball tip of the glass cutter before trying to break it really helps.
If you are cutting anything with a curve (or even straight cuts that are narrow), try flipping the glass over after scoring it, laying it on a flat surface, and pressing with the ball tip of the glass cutter along the score line
to run the score. If you are cutting an oval, circle, etc., make several break away cuts out from the score line before you turn the glass over.
I found that holding the glass cutter backwards from the way that you are supposed to hold it worked the best for me - but then I tend to do everything backwards anyway.