The club head should be descending at impact with the exception of the Driver and the Putter.
What is meant by descending angle of approach? Many players do not truly understand this term, and its meaning. Some think it is hitting down on the ball. Not So! Trying to get the ball airborne is the move that disturbs this club head path. The loft of the clubface is sufficient to lift the ball. Attempting to lift the ball tends to open the clubface which will slice the ball and lose distance as well.
To have a good angle the left leg passes the ball first, hands second, and club head last. This motion automatically moves the club head in the descending angle of approach. Having the club head passing the hands prior to impact creates an ascending angle of approach. Most of the time with this action the club head will hit the ground behind the ball (Chill dipping) or the swing bottoms out early and the ball is struck on the upswing, topping it.
To check your club head angle practice the 'hit and hold' drill. This will give you immediate feedback in determining whether the clubface is preceding the hands at impact. Hit a few balls and hold, not allowing your hands to go past waist high on the follow-through. If the left wrist or hand is bent forward this indicates the club head was ascending rather than descending at impact.
Final note: You cannot cheat this drill, as it will clearly show you where you are in regards to your angle of approach on your golf swings.