Underside of the sandals
It resembles the feet.
Underside of the flip-flops
It’s wide, has no distinct shape, looks like the ovals.
Underside of the moccasins
It narrows at the bottom, the curves are less distinct.
They are thin and straight.
Straps of flip-flops
Draw the semi-circular strips as it’s shown in the picture.
Upper part of the moccasins
Separate it with the help of the slightly curved lines.
Improve the drawing
Draw the sandals’ buckles, the flip-flops’ straps and the moccasins’ back part.