For HSIE subjects, if you run out of time at the end (where the essays are) just write dot points to finish and a short conclusion tying everything back together. Some people like to do their HSIE exams like this: Essay -> some short answer -> some MC -> finish short answer -> MC - > essay, just to "break things up" so your hands don't get too tired doing 2 essays in a row. This ensures that the short answer/mc are sandwiched in between and you've guaranteed that you've attempted everything. I never did this cos I'd probably forget where I was up to and end up getting stressed but my friends seemed to like this strategy.
With English, don't put yourself in the position where you're strapped for time! Time goes really fast in paper 2 so make sure you stick with 40 minutes per section. If you feel like you're lagging behind, then with ~3 minutes to go in each section, quickly wrap up your paragraph, and if you had another paragraph planned, write it in like 3 sentences, then write like a 1 sentence conclusion which fully answers the essay question just to wrap things up.
For maths, it can be hard at the end as you might have a bunch of unanswered questions which you're just stuck on. I'd try to get something written down for each question, and then come back to the question you might have a shot at.