Read The Womanly Art of Breast Feeding.
Start hand expressing from 38 weeks, you might get some colostrum and you’ll get more colostrum when baby is born and milk will likely come in quicker (waiting for that is when people often crack and start formula). There are videos on YouTube.
When baby arrives and you are wondering what you are supposed to do with it, the answer is latch on and allow them to stimulate milk. All newborns do is sleep, snuggle, suckle and fill their nappy, if it seems that they are on your breast all their waking time then that’s great!
Accept that for the 4th trimester, you’ll be feeding, feeding and feeding! Give in to the mess and getting nothing else getting done and just enjoy the closeness and the snuggles for what is just a snippet of their lives. You’ll be tired, but allow yourself to be tired, laze around and just make you and your baby’s comfort the priority.
In terms of practical tips, I’d just accept that the success of feeding depends on feeding on demand, directly from the breast as much as possible (if exclusively is not possible). You produce milk in the quantities that baby demands, making watery thirst quenching milk at the beginning of the day, thicker more filling milk at the end (so you also guide the sleep/wake cycle by feeding too). When you start expressing you mess up these supply/demand and day/night milk type relationships and it can all go a bit wrong. For example a common problem with expressing is creating increased or over-supply but the oversupply is of watery milk which gives babies colic and poor weight gain. Poor weight gain makes people feed even more, worsening the situation...the whole thing being a really common reason for bfing to fail. All started by expressing. The other common reason is trying to feed to a schedule instead of trusting that you and the baby can find your own, and understanding that feeding clusters are totally normal.
I have 3DC, all breast fed. I’ve learnt more each time, from personal experience as well as watching how each set of mums I’ve shared my mat leave with each time and I’d say that those who’ve been most successful have been those who have just relaxed into feeding in demand, anywhere and anytime without schedules, expressing, bottles and all the things people try to sell you (because they can’t push formula).
The last thing I’d say is that nature is sadly fallable. Breast feeding is the normal, natural way to feed, but fed is best. If you need to use formula don’t beat yourself up; we live in an age when this is an option and this is a great thing!