Tracing your pattern accurately is a very important step in the stained glass making process. I often watch people rush through the tracing of their patterns and end up with clunky representations of what they are trying to make.
The first important rule of tracing is that straight lines NEED to be made by using a straight edge. I care don't how good you may be, your interpretation of a straight line will never be as accurate as a line made with a straight edge-- and trying to grind crooked line straight is one the the toughest things to do.
The second important rule is to place your hand inside of any curve you are tracing rather than outside the curve. In the diagram below the hand rests incorrectly, outside of the curve making it necessary for the entire hand and arm to move the complete length of the curve being traced. There's an easier way.
Simple tricks like this can make your patterns much more accurate and lead to far less time consuming grinding at the grinder.