Keeping your body narrow on freestyle makes hydrodynamic sense, but how narrow IS narrow?
Why do it:
The less area you expose to the standing water, the better able you’ll be to slip through the water with more efficiency and speed.
How to do it:
1) Start by swimming smooth freestyle.
2) You’ll need to imagine you’re swimming down a tube, with your entire body.
3) Make sure you extend your arm directly forward on each stroke.
4) Keep your head still and in line.
How to do it really well (the fine points):
Have a coach or friend watch you from the end, or from above. Is your body hidden behind the line of your hand, or arm? When watching from above, are your arms parrallel or directly in line with the lines on the bottom of the pool? Visual feedback will be key in this, as sometimes what you’re doing isn’t exaclty what you feel like you’re doing.