I think the best way to prepare for your further SAC is practice. In addition to this, it is also vital that you go through any practice SAC questions or textbook question, ensure they are marked and to also note down how and why you got these questions wrong and try and not make the same mistakes next time. You can also add these to your summary book as there is no limit to what you put in there as long as it fulfills the requirements.
If you are fortunate enough that your school provides you with past SACS, like mine, try and complete them first before completing VCAA Exams. The reason is often schools make their SACS somewhat different to VCAA exams but quite similar to previous years' SACS. SACs are generally harder than VCAA exams for scaling purposes and VCAA exams may not be the best way to prepare yourself for tough data analysis questions. If you can you can go to VCE book shops and buy other further books such as NEAP, insight or hefferman as they are quite challenging. Doing them will increase your familiarity with challenging questions. However, if none of this is possible then just complete VCAA exams.
Data analysis also requires a lot of interpretation of data. That being said, these interpretation questions can also be answered with a generic answer so ensure that you place these templates which can be found in your textbook into your summary book. This way you can simply flick to them during the SAC and it will save you a whole lot of time and hassle from trying to memorise them. Best of luck with your SAC!!