My biggest "AHA" was figuring out what "wings' level" truly means... a number of years ago Iwas told of a good trick to figuring out what wings level meant by a good friend. None of the people I'd flown with ever mentioned to me, or told me,a way to figure out what it meant but all it took was this "AHA" moment from a friend while practising for the Australian Nats back in 1998 (or 1999). He noticed that on just about every push/pull Iwas using a lot of rudder to straighten my vertical line and he told me that it was because my wings weren't level. Since then, and using a lot of practise, I've gotten a lot better at not using rudder during those pulls/pushes because my wings are "level".
So what's the trick? Ican't tell you - might have to fly against you one day!
Kidding... the trick/secret is to always look for your outboard wing from underthe plane. If you don't see it then your inboard wing is low and if you see too much of it then your outboard wing is too low. You just need to figure out, based on your own plane, what level really is and then ensure that you only have "so" much of that wing on the outside showing when you fly across the box (left to right, or right to left).