I am doing Combined Law in 2004 at USYD. I stuffed up MOST of my first assessments in 2003:
subject: mark (rank)
4 unit maths: 75% (7/21)
Physics 81% (23/70)
Chemistry 81% (29/70)
English adv 80% (55/150)
IPT 91% (2/20) ---> This subject din't count for UAI tho
3 unit maths 100% (1/70) ---> I only lost 3 marks all year.
I screwed up 8 funking units worth, and I was seriously feeling down. It cost me 99.70+ UAI.
I absolutely blitzed everything for all subjects after that and got a UAI of 99.65. So there is hope even if u screw up ur first assessments. Oh, btw, by blitzing I mean: Top 3 in every assessment and in HSC in every subject after first assessments, except Eng Adv trials (I came 25th).
My advice to get 99.70+:
1. Try your absolute best to get band 6 in English Advanced. It will go a very very long way to getting 99.70+. According to SAM, my UAI would be 99.80 with a band 6 for EngA.
2. Work very very hard, I mean realllly hard at subjects you are weak at. For 3 weeks before HSC, I studied 15 hours/day, MOST of which was English. After a LOT of hard work, my EngA exam mark was only 89, but incidentally, this was the 3rd highest mark in our school in the HSC, so I felt pretty good.
3. Do not screw up trials (usually worth 40% internal) or the HSC. I screwed up EngA trials, and paid the price. Learn from mistakes in less weighty assessments. Do a funk load of practice before trials and HSC. Make sure you go through any probs with ur teachers.
4. Don't think scaling will help you if you do "high scaling" subjects (excepting of course 4 unit maths). My physics/chem/3 u maths/IPT/EngA HSC exam marks were pretty much the raw marks I expected to get in them. Aim close to 100 % raw in every assessment in every subject you do (except, again, 4 unit maths).
5. Make notes and study all the way through the year. If you want Chem/IPT/Physics notes or English Advanced essays, just ask me. Put notes into your own words. For maths, do a heck of a lot of practice. For 3 unit, do heaps of Q 6 and Q 7 practice for trials/HSC. For 4 unit... practice a lot and try your absolute best, that's all you can do.
Sorry for the excessive length of the post, but I hope that I have been able to impart some helpful advice.