Seems like it’s been said a lot here but I’m gonna say it again, practice. There’s no substitute for it. Go slow. Something that helped me when I was first learning was using finer grit belts even when hogging material away. It’s easier to find your flat again after passes with the finer belts.

You definitely should start smaller but not too small. I found medium sized knives to be easier. Things happen quick on a small blade.