One way is to look a knife publications, like the 'Knives' annuals.
If you see knives that light your fire, sketch them out, putting in your own ideas. Let the drawing set near you for a week or so. You will begin to see things that you originally thought were great, as not so hot. Change these things to suit you, and leave the drawing where you can see it. Sooner than you think, you'll have a pattern that you like, but that does not resemble the original too much(which is a good thing).
I make my patterns from 1/8" acrylic sheet, and handle the pattern for awhile to see if it will work out, or if I will stil like it after a week or so.
Another thing is, just do a lot of reading. Read every knife magazine, and publication you can get your hands on(both on current, and historical knives). Study the photo's very carefully. Pretty soon you will develop a discerning eye for what's good, and what's not(to you at least).
Start sketching all your ideas out. The more you read, and sketch, the more ideas will come to you. Some even keep drawing pads beside the bed, so as to put down ideas that occured to them in their sleep.
Good luck to you.