Attach the foam to one piece of cloth by simple running stitch so that it doesnt move while doing embrodiery. Attach the ring and start working feather stitch -any design of your choice. I have done simple feather stitch square pattern and used chain stitch to form flower like design in a different colour thread. Check Veena's step by step pictorial instructions for feather stitch embrodiery.
Stitch the second piece of cloth covering the foam on the reverse and invert it so that the foam is in between two pieces of cloth. Give a stitch in the inner side so that it stays stiff.
Repeat for more coasters.