As you pump continue the massage if possible. Once the initial flow slows down or stops, take down the breastshield and massage your breast for a few more minutes. Begin pumping again. If using a single pump, switch sides as soon as the flow begins to slow and back and forth again as needed. Some mothers have found the homeopathic remedy known as Rescue Remedy to be helpful in aiding the letdown response both during pumping and nursing.
Some moms find pumping is easier if baby is nursing on one side at the same time.
You also may have better pumping results in the morning hours when milk supply is greatest. A lot of moms pump about an hour or so after baby's first morning feeding. Should your baby want to nurse soon after pumping do not be afraid to put him to the breast. Never pump longer than 20 minutes at a time. If pumping is painful, something is wrong - either you are using the pump incorrectly or your pump is an inferior one.