A lot of times when people are first learning to wheel walk, their feet aren’t quite right and it throws everything off. The following advice has helped a lot of the people in my club. Hope it helps you, too.
When you wheel walk, you need to make sure that your feet are straight on the wheel, not turned out like penguin’s. (I know it sounds funny, but it’s a very common mistake.) Also, be sure that you’re propelling your wheel with the balls of your feet instead of your heels (another common mistake). Other than that, just practice, practice, practice.
Do what they said, plus this:
Learning to wheelwalk can be broken down into two main parts: foot control and balance. I’d start by breaking down the two and learning them separately. That means finding a wall that you can lean unto and wheel-walking along it. When you can do that confidently, start letting go and riding away from it. It’s a lot like learning to ride.
Balance can be practiced by riding normally, but very slowly.
And always remember to keep your back straight. You’ll be doing stand-up wheel-walking before you know it.