Will laying on your stomach help with not getting a seroma after a tummy tuck?

Thank you for sharing your question.  Though laying on your stomach would apply external pressure to your skin it is unlikely to make a material difference in the formation of a seroma.  You are better served with a compression garment that can provide pressure and can help minimize sheer.  Hope this helps.

Lying on your stomach should not impact you developing a seroma or not...................................

Thank you for your question.
There are no well designed studies that support laying on your stomach to reduce seroma formation.  Could it work? Possibly.  Could it be harmful? Possibly. 
The reality is that during sleep we all move around quite a bit and therefore any compression from laying on your stomach would not be uniform and might actually produce shear on newly forming connections between abdominal wall and skin.  Every surgeon will have a different protocol. Personally in the absence of good scientific data I advise patients to do what's comfortable.
Best Dr. L