Read all the instructions that come with your pump. It is important that the pump is put together properly, and that you use it properly so you do not injure your nipples or breasts.
Follow the cleaning instructions. Make sure you wash your hands well before handling the pump parts.
You can express breastmilk at any time. You may find it easier to express right after feeding your baby. Do not pump right before a feeding unless your breasts are very full and your baby finds it hard to latch.
If your baby is not breastfeeding at all or very little, express both breasts every 3 hours.