It is helpful to follow the same routine each time you express milk. Drink plenty of water and never ignore your thirst. At first it may be necessary to pump every 2-3 hours to maintain your milk supply. It is very helpful to think of your baby when pumping.
Some women bring a clothing item from the baby to work.
The touch and smell encourages the milk ejection reflex. Massaging your breasts while pumping increases production. A shortened pumping session is better than not doing it at all.