Choosing a knife. The type of knife you choose will have an incredible impact on how much you’re able to enjoy knife throwing. Keep in mind that quality throwing knives do not have a handle. The blade is the throwing knife.
▪ Size: Knives that are between 12”-16” are a good size. They aren’t too big and not so small that you’d have to throw harder and strain to watch them in flight.
▪ Weight: Knives of the above size will fly fairly undisturbed from wind and make a satisfying sound when they hit the target.
more at http://www.articlesbase.com/extreme-sports-articles/knife-throwing-so-you-want-to-be-a-knife-thrower-470112.html
I ordered a set of 11 ounce Pro Flight throwing knives from The Great Throwzini and they seem just right. (Earlier, I bought a set of lighter knives from a different vendor and they just didn't have much sticking power and just seemed harder to throw.)
You should spend time thinking about the target. Soft pine works much better than a plywood sheet. The plywood is pretty hard so getting a consistent stick can be difficult.