As someone who interviews people as part of my job I'll add a few tips.
When talking about negatives, it's always bst to refer to them as "areas for improvement". It's great that you have identified something that you could improve on. Rather than say you have diffilculty delegating, say delegating is always a work in progress, because you believe in order to delegate you need to do the task at least once to ensure you are being clear in what you expect when you do delegate.
Try and think of anything that you personally would like to be better at and what support you think you would need to be better-this will throw up loads of questions for you to ask.
What training is available? Are there opportunities for outside training to help you progress, and would they support this? Again, good questions to ask.
Don't be afraid to write your questions down prior to going in and referencing them at the end. And remember, an interview is not just about whether you are right for them, but whether they are the right company for you-it's a two way thing. Good Luck!