Hi acedemic_achiver
I did the JMSS entrace exam this year and got into interviews. I strongly recommend the edutests practice tests and making sure u have a good speed for the questions. I think there might be some tips posted on another thread of mine but basically, PRACTICE YOUR MATHS. Get comfortable and dont be intimidated by the questions. I studied 3 months in advance and did not do any tutoring for science only maths for the first month to make sure I got the hang of it (for reference I got a below average during the selective exam last year)
The exam (if you did the acer one this year for sehs, it was easy) doesnt go too in depth , like the questions are pretty shallow its just that there are a lot of them... Timing is a huge part of it.
For the writing portion make sure you know how to write a discussion and practice just writing in general to build up ur skills. They were pretty generous with the time with 5 min planning given and 30 min writing. Read articles and watch videos (veritassium and ted ed), EDUCATE URSELF on world issues. Be a woke teenager.
Best of luck and hope you get in!