Wanting to breastfeed my 2nd child. Any advice on how to have success this time around?

I have a 2 1/2 year old son and I attempted to breastfeed him when he was born. I gave him nothing but breast milk and did not offer any of it in a bottle. However, my breast milk took what felt like forever to come in and at around 5 days old he became very dehydrated and I was forced to give him formula. I attempted to continue breastfeeding while bottle feeding but eventually I gave up at 5 weeks because my breast milk just didn't seem to be enough food for him. I don't think my milk ever fully came in and the poor little guy was starving. I'm now currently 24 weeks pregnant and really want to avoid formula altogether. Is there anything I can do to encourage my breast milk to come in faster? I'm barely a B cup, would this have anything to do with me not being able to produce much milk? Any advice would be greatly appreciated!