Stand in the trap bar and deadlift it to lockout and then shrug the weight up with your traps. Really contract the traps and try and bring the shoulders up to your ears. Also let the weight stretch your traps as this is what will cause the most growth. Huge traps lead to a huge squat.
Tips: Try to keep your arms straight so you don't cheat by using your biceps. Don't roll the shoulders, move straight up and down.