Take one nipple between the thumb and forefinger, and roll it gently between them.
Gently pull the nipple, down and out, from the areola, and over the nipple, causing it to become erect. If doing it orally, lick (or gently suck) the nipple until it is erect. If using a breast pump (a device used to express breast milk), pump a few times until the nipple is erect.
Once the nipple is erect, continue stimulating for about a minute.
Then leave the nipple alone for about 2 - 4 minutes.
After this time has elapsed, go the other nipple, and repeat the same procedure. Waiting 2 to 4 minutes afterwards.
Return to the first nipple, and repeat. Keep going from one nipple to the other, with a rest in between.