Once you have the knife in your hand you will immediately feel it fits perfectly or uncomfortably. It should feel comfortable as a natural extension of your hand. It must create trust, not fear. If it feels wrong go to the next one. When its the right fit start cutting and see how it relates with the other devices.
Weight: You will need to try several blades to get the perfect weight. It is believed that a chef's knife cuts better since it "falls" with more force. There are those that say that a lighter chef's knife will flow more freely and you will be able to move the knife more skillfully. Go for a style that suits you.
Balance: "Perfect balance" is in hand of the user. Look out for the balance by holding the knife. If it feels awkward on the handle or blade, it might not be good for you. You use more force with an unbalanced knife. Balance is important. If you use it, the blade should not feel unstable, as if it were trying to turn to one side or the other.
Size: The 8 inch chef knife is the most popular among home cooks due to its versatility. A longer 10-inch knife can cut a lot more, but it can feel embarrassing. A 6-inch chef's knife set can offer an element of portability, like a chopping knife, but fails when you're working with volume or slicing something the size of a watermelon.
Incase i left out some, what would you look out for in a knife set?