Tummy Time Help Please

sunflwra

Hi Ladies-

LO is now one month old and the pediatrician recommended starting tummy time each day.  I have a Tiny Love play mat with a little U-shaped pillow but I'm not sure how best to put LO on the mat.  Do I start her just on the mat itself and then graduate up to the pillow? Should I be laying her flat on her tummy or tuck legs under, etc.  She's already got a really strong neck, so I'm excited to introduce this with her, but just want to be sure I'm approaching it the right way.  Any help is appreciated- thanks!