For larger ones I kind of use Tartans method. I use stabilizer instead of dryer sheets and i put water soluble thread in my spool holder and regular thread in my bobbin and stitch a closed circle, then trim, slit, turn right side out, carefully with a DRY iron set your shape, then turn on the steam and blast...then pick out your bobbin thread and remove your stabilizer or dryer sheet.
NOTE: don't forget to mark this thread and keep it seperate from your sewing threads...I have heard of people making a mistake and using the water soluble thread for peicing. then they finish their projects, wash them and oh what a mess.