1. I have them start out standing
sideways to the target in the Set position with their hands at
their belt buckle.
2. They then lift their GS leg
vertically up
to Balance Position, with their GS upper leg horizontal and their
GS lower leg and GS foot hanging down vertically below their GS
knee. At this point, their hands are still at their belt buckle.
3. From the Balance Position they
break their hands and start to vertically lower their GS foot again and then, when their
GS foot is 9 or so inches above the ground, start to stride toward
the target. In other words, the GS foot goes vertically up,
vertically down, and then out toward the target. As with the Foot
Flip Drill, I
have my guys focus on keeping the side of their GS foot pointing
at the target, their GS toe pointing at 3B (1B if they are
lefties), and their GS foot just 3 to 6 inches above the ground as
they stride.
When my guys are doing the Sideways Stride Drill, I
also have then pay attention to what their shoulders are doing.
With my younger kids (e.g. under 11), after they break their hands
I have them focus on pointing their glove at the target. With my
older kids, after they break their hands i have them point the
glove just to the right of the target (or just to the left of the
target for lefties) as Mariano Rivera is doing in the photo below.
4. As they stride toward the
target and their GS foot rotates and then plants, I have my guys
focus on keeping their glove pointing at, or just to the right (or
left for lefties), of the target until their GS foot has completed
planted as Justin Verlander is doing in the photo below...

What keeping the glove pointed at
the target does is help to keep the shoulders closed as the hips
open up underneath them. This will then allow the muscles of the
hips and torso to powerfully pull the shoulders around (which is
the definition of throwing with the body and not just the arm).

It isn't a coincidence that if
you look at photos of extremely hard throwers like Joel Zumaya,
you will see their hips rotating well before their shoulders.
5. Once their GS foot has
completely planted, with the GS toe pointed at the target, my guys
then let their shoulders be pulled around by the muscles of their
hips and torsos and throw the ball.