The essential parts of a knife are the blade and the handle, so this is where you should focus most of your efforts. If you want to spend time on guards and pommels and such, that's good too. I don't make them because I don't have access to soft metal (brass, copper, aluminum) and I don't have a band saw. For the design of this knife I had a freehand rendering that I drew in English class under my desk that I used as a template. I liked the basic proportions, but I needed to increase the scale by 75%. This made the knife too big for graph paper so i had to tape some together.
I started with the handle. Working off my original sketch and with lots of measuring, i drew a full scale rendering of the handle. To make curves I draw dots at the correct measurements, then connect the dots with a French curve. This is where a lot of personal preference comes in. Design what you like and what looks good, it's your knife!