Give yourself enough time to practice pumping and get your body used to pumping before you return to work. Start pumping or expressing milk for storage to use once you return to work. At first, pump once a day. Early pumping sessions help your body learn to "let down" to a pump. This allows you to store milk that the care provider can feed to your baby while you are away. Many find the best time to pump is in the morning. This is when milk production tends to be greater.
Pump about 1 hour after you have breastfed your baby. Slowly increase to 2 to 4 pumping sessions per day. But always feed your baby first. Don't be surprised if your baby wants to breastfeed more often for a few days whenever you add a pumping session.
You can use the double collection kit to pump both breasts at once. But some choose to pump one breast as their baby breastfeeds at the other. This method has the benefits of double pumping and it may interfere less with your baby's breastfeeding routine. Your body may learn to let down in response to the pump more easily. If you try this, switch the breast being pumped as you increase the number of pumping sessions. You still may want to include a few pumping sessions using the double collection kit before you return to work. Ideally, you should store at least 2 days' worth of feedings for your baby before returning to work for peace of mind.
Remember, you will bring home a day's worth of milk every day once you return to work. You don't need to stockpile a whole freezer full of breastmilk.