I’ve found it hard to find a good how-to for the manual (coasting wheelie). The point is how much you can move your body in order to actively control the forward/backward balance. If the front end goes up too high, you need to thrust your body forward to lower it. If the front end drops too low, you want to pull back your hip while also kicking your feet forward. You could adjust the balance by tapping on the brake or pedaling, but keep it for the emergency only because it slows your progress if you rely on it.
This clip is an extreme example, but it nonetheless shows what actions are taken while I was manualing over an uneven terrain. Hope it helps.