Wait until breastfeeding is well established with a good, easy comfortable latch and let down.
For some moms, a comfortable latch and let down may take a couple of weeks, and for some others, up to 4-5 weeks.
The first time, you may want to pump 1-2 ounces and then give the baby that feed in a bottle. If you are going to use formula, prepare a small 2-4 ounce bottle and give it to the baby at regular feeding time. Be sure to pump the breast to compensate for the missed feed. Don't be surprised if your nursing baby does not want to take the bottle from you. You may need to hand baby and bottle off to someone else to do this experiment!