Here is the way I play when the lie is not flat without being too fancy. To me,

Ball above feet (I think this is what you are talking about)-
1) Grip down the club slightly
2) Stand slightly taller and imagine you are hitting the ball off a tall tee and that you must "sweep" the ball.
3) Swing.

For the shot above, the ball will tend to draw so aim more to the right. The more the ball is over your feet, the more it will draw so aim accordingly.

Ball below feet -
1) Grip the club normally
2) AsLowpost mentioned, bend the knees more and feel like you are letting the arms hangdown more.
3) Swing. It is extremely important to keep your head down, otherwise your will definitely hit it thin.

the ball flight is the opposite of ball above feet.

If you thinking its already going to be a fat or a thin shot, then you are most likely going to do that. The most important thing for any golf shot is to imagine what you are going to do.