Knowing a first-hand experience of the whole selective examination process really would've been helpful right now for me less than a couple of months ago, so this is making up for that!

First and foremost, preparation goes a long way. I would definitely recommend an external tutoring company as they'll most likely be your best chance at success; They know the content (or, at least mostly, from other people's insights) and know how to answer it. Personally, I contradicted this statement completely, not having an understanding on just how serious others were studying for this test. Although, not necessarily to my downfall as fortunately I was given a first-round offer- but- this was blatantly because I was hanging onto my English skills for dear life.
For a not-so confident student, 3 months of study at a minimum is encouraged as you'll be competing against students with potentially years of prior tutoring. Again, take this with a grain of salt as study is personal and I, myself, took an unconventional route- pretty much study until you are comfortable with any practice tests you could be given for each category.
*Also note that the tests look VERY different to the practice tests currently (As of the time I am writing this) available on the VIC Selective Entry site, due to the switch to ACER for administering the tests.

Now onto the tests themselves:
Reading Comprehension:
RC went down very much like how you'd expect it to. Big blocks of text and questions. Some required you to interpret a table which, I struggled with, but it only had 2 or 3 questions attached. Do not bother reading the texts, first, look at the questions then skim for answers. However, for the poems, these are a bit more tricky to understand, read through them entirely then give it your best shot, these texts are not as straight-forward and will require some educated guesses.
Mathematics:
Do not even get me started on mathematics! Probably the hardest test for me and I legitimately only answered 2 questions and guessed the rest. Sounds a bit pathetic but there are for sure better mathematicians than me out there. My tips for this one are, do not panic, remember your strategies for problem-solving and USE YOUR PAPER. Actually write on the test, something I did not thing to do like- DUH- to work out problems. Regrettably, I believe if I had kept my cool I probably would've done better. Things like pie charts and ratios are on the test and, overall, the questions are delivered in a really "creative" way (i.e. confusing terms, lots of visuals) so they look really intimidating but are actually possible to solve with some thinking.
Reading - General Ability:
This one was a good test. For an avid reader, I had such a big advantage with an extensive vocabulary. There were questions like, which two are the most opposite, what does this word spell if you unscrambled it, what word is most similar in meaning to (blank). For preparation literally just read. Any books will do whether they're fantasy or non-fiction- just build your vocab.
Quantitative - General Ability:
Another bad test for me- although slightly better than mathematics. For this, I recommend all the practice questions you can get your hands on as well as recognising strategies to solve these logical types of problems. Otherwise, not too much to say on this one with a couple fill in the (number) questions in sequences and pattern recognition.
Writing:
For the writing tests there were two text types you were expected to write in 40 minutes with the allocation of time left up to you. (Meaning you could evenly split your time 20-20 or do something really left-field like 30-10.) These were a persuasive and creative piece on a given prompt. Both of ours was a picture with the persuasive having a tiny bit of background context also on it. My tips for this test is practice writing in 20 minutes and producing something decent. Also, with your ideas, go big and bold. On the test paper they say "be creative" just make sure there is some sort of conclusion (which can be a cliff-hanger) at the end. For the persuasive it is easy, or, at least it was for me, to lose track of time. Plan 2 arguments and possibly at rebuttal (still in favour of your stance whether for or against) but QUICKLY. Make sure to be concise and succinct and use your time well- just go, go, go!

Hopefully this gives some insight into the ACER selective entry exams and just these types of exams in general. Remember, this post is not the be-all-end-all. I am just simply sharing my experience in 2024. Good luck for any future entrants and just keep calm and carry on throughout the exam!