By the sounds of it, you're well on track to get good grades! I personally only did one sorta-essay subject (Media) amongst a sea of sciences.
Generally, I found it helped if you stay on top of your coursework (try and get it in early if you can) as well as homework.
Always push for feedback in essays and try and take it on board.
If your teacher is lazy with marking, bug them every day until they get it back to you (media teacher: you need to bug me. I know you're good at that)
You don't necessarily need to do past papers if you're good with essays, but make sure you're familiar with what they typically ask and how they ask it. Examiner Reports are also worth a read.