Dot Point workbooks are good if you do the questions and get them checked and marked by a teacher or a tutor (lol) regularly. Personally, I found that this worked best with Chemistry, and that it didn't work at all with Physics. Do not mark your responses by checking the solutions at the back of the book though, because those ones are often just silly.
You don't really need tutoring for science based subjects, since the HSC is mostly about content. Just refine your long response skills, constantly revise the content and you'll be set. If you do find that you are falling behind, then tutoring will probably help you a lot.
Maths tutoring may be necessary if you are either falling behind or if you really want to be competitive. However, most of your improvements in maths should come from self practice. Do a few textbook exercises if you need a better understanding of a certain topic. Once you have everything down, go straight to past papers.
As for English, I'm not sure. Quite a few say that tutoring does help, but quite a few also say that it's pointless. I found that when I left English tutoring and started simply sticking to routinely writing and sending one essay to my teacher every week, my ranks improved a lot (went from rank ~150 to ~50 in English in around half a year). However, this might be quite difficult if your own teacher tends to not respond to your essay submissions or gives poor feedback. In that case, tutoring might help.