I generally pick a part of the knife as a starting point handle, finger choil, ricaso, etc. Then start drawing it on my pad. Once I have what I want, I make a wooden one to see how it feels. If I need to modify it, I do it to the wooden one.
I have a bucket full of rejects for the grandkids to play with. Other times I just grab a piece of steel and start forging. They are one of a kind custom forged knives. LOL
In my intro class at Haywood Jason Knight, MS sad to us "if you can draw the knife in your mind on paper you will make great knives" or something along those lines. In 17 months I have about 20 note pads full of knives the first 6 of them are worthless, the next 10 are about 25% viewable, the last 4 have about 75% good ideas (starting points). My current pad has 14 pages worth of drawings to date, 11 pages are good.
I have forged about 60 knives to date, Number 60 is the best one yet. I was having lunch and drew it on a paper towel in the dinner. Got home and transfered my design to 5 gallon size paint stiring stick, grabed a Heller Rasp I just gotten, triple anealed it and then started forging the shape, finger groove gills, & bevels, in the end my 2013 Neo-Tribal KITH knife was born.
I draw at least 10 knives, 5 days a week. Good relaxation and it works for me.