Yes, practice is definitely what I need the most of! Right now it's all unfamiliar enough for the unbalanced moments to be happening for all sorts of reasons, not just being on the wrong diagonal, but I know with time it'll come to me. I do latin and ballroom dancing at university, so I know how it feels when practice makes something click. I was never very co-ordinated until I started dancing, so I'm hoping that as I grew my dancing feet, I'll grow my riding seat and things will just become natural and instinctive.
I've already noticed, however, that I have a tendency to look at the horse's right shoulder every time, rather than his outside one. Must curb that before it becomes a habit and I'm on the wrong diagonal half the time!
I'm also having trouble with losing my stirrups a little sometimes, having my foot slide about in them. I know from my instructor that dropping my weight into my heels will stop this from happening, but right now I seem to be tensing my legs up quite a bit, stopping me from doing that! I know that practice, practice, practice is the key, and two lessons a week really doesn't feel like enough when I'm itching to get out and learn every day!