If making a left turn from a left lane, you want to be in the left third of that lane. Depending on the lane width, in a narrow lane (too narrow to share side-by-side with a car and still keep about a 3-foot separation) position yourself in the center to control it. As far as how close to the intersection itself, you to be just behind the stop line, if there is one, or move forward to where you can make your turn and get quickly into your new lane when oncoming traffic clears. If there's a traffic light, it's probably safer to do the former so as to avoid getting caught out in the middle of the intersection when the signal changes.