Make the most of "bludging' and just enjoy it. The only significant step up I noticed in year 10 was English, compared to the other junior years. The assessments became more difficult but as long as you follow the criteria and marking guidelines you will be fine. As for studying, don't stress yourself out, I found that I only needed to revise in the 2 weeks before exams and I got straight A's, in the ROSA too. Make sure you get on top of assessments as soon as you get them though as they tend to come in blocks and with poor time management it can be very stressful.
Use year 10 as a springboard for your senior years. Start developing habits but don't go all out so that you're not burning out towards the HSC. See which subjects interest you and have a vision of what ones you would like to do. Just make sure that you start looking at English with real importance as it is no longer becoming just another subject, instead it is one of the keys in attaining the ATAR you want.
Most importantly have fun and make the most of your last year as a junior!