Here are a few basic tips for successful sawing. Match the saw blade to the gauge of metal that you are using. Ideally the thickness should be equal to two teeth of the blade. Make sure the blade is straight and tight in the saw frame. It should "ping" when plucked in the frame. A loose blade will break very easily. And finally, let the tool do the work. Do not push too hard on the frame while sawing. Ease up on the frame and the blade will slide more smoothly through the metal.
Another essential cutting tool for making straight cuts in metal is a shear. From hand shears to a table shear, Jewelry Tools carries a variety of shears for assorted metal gauges.