The foot control is all about toe-heel, toe-heel, toe-heel. Don’t try to wheel walk flat footed and using only the middle of your foot.
Everyone is going to say to lean back like it’s some magic fix. That advice is overrated and I think bad advice. You do not actually lean back while wheel walking. It’s just a very slight weight shift to counter the weight of your legs out front. The weight shift can be accomplished by pushing your butt out like you’re trying to make your butt look as big as possible.
For me the most challenging part of wheel walking was learning the foot control and getting to the point that the foot control became second nature (so I didn’t have to constantly think about it).