After the keiko he gave very valuable advices on the correct fumigomi and the practice for it, which I will describe in the following.
Step 1: Take one large step forward with the right foot. One main point is that when the right foot makes contact with the floor, there is a sheer-like force going, not straight down, but forward-down as shown in the picture below.
Step 2: Quickly draw the left foot to the right one, and stand on the soles of the feet, so that the body is going slightly up.
Step 3: Repeat the exercise.
This is really the tip that I have been looking for to improve my men-strikes, for a long time. So I'm eager to share with you guys here! Hope it helps!