Adding on Angelina's superb advice, some other things to look out for might be how each character's use of language changes (or doesn't change) throughout the play, particularly Prince Hal and his use of soliloquy and other language/dramatic techniques when contrasted to characters like Hotspur, who at one point states that he "profess not talking" (He doesn't speak well).
In terms of structure/form, there's definitely a lot of flexibility and ways to interpret meaning. For my HSC, I decided to focus on performativity and argued that the use of a play extempore (play within a play) served as a structural technique which symbolised a turning point in Hal's growth into a Prince, where I used language (eg. "I do, I will” / “and take thy praise with thee to heaven!”) to evidence his growth and fulfillment of the chain of being compared to Hotspur's ineloquence.
Hopefully that gives you some ideas on the sort of ways you can interpret the play's structure/form/language and how that ties into the wider themes. I'd definitely recommend you read lot's of critics articles to find some interesting and original takes on the play, as I found that helped me a lot in understanding and developing my own views.
Good luck with your HSC!