Hey there vennmeh! I was quite worried about applicatiosn like you earlier too because I didnt have any prominent leadership roles like SRC/Prefect etc and Iknow lots of those pople applied from my school. So dont worry too much about that and just talk up some of your current extra curricular activites - any music/sport/community service/exchange/work experience. I also suggest if youve time and are keen do try to get involved in some volunterring/work experience position in the summer holidays if you dont have much.
For the application, I thin it's really important that you really let your own voice shine through (gosh so cliche but so true). I think the people going through hundreds of apps want to hear from YOU and not read what you think they want to hear. It'll really differentiate you from other applicants. Also research the firm and the industry so you sound like you know what you're getting into and try to mention something specific about the firm in your anwer. And always try to use up to character/word limit! And if you have won some pretty amazing awards, dont be shy and just tell them about it because you dont want to undersell yourself but dont exaggerate.
I think PWC/EY/Deloitte all had group assessments this year and KPMG had one previously but changed it this year. They all have 1-2 one on one partner intervews. Once you get to the interview stage, they're really into getting to know you as a person so they cna see if you can fit into their company culture. So lots of the interivew questions are behvaioural questions - they often as you about a situation where you demnstrated some of the firms vlaues or the skills required to work in the industry e.g. tell us about a time when you had to work in a team and someone slacked off/your life changed significantly e..g new school/country/deal with lots of things gong on and stress/time management/wne you had to be sensitive blah blah and how you dealt with these situations. A diverse range of scenarios is advisable so have an idea of all the thingds youve done so you cna draw on the best one to answer the question. Also dont just tell them about the event, tell them what you leanred from it and how it impacted on you , they really like to hear aobout personal growth etc.
For group assessments: thy're pretty fun and just be a team player - dont be shy but dont dominate. You'll oftn be role playing and they deliberately gives you roles that'll conflict - so negotiate and compromise
And just generla basic interviews tips: be on time, smile and look like you want to be there, ask questions!! (in my partner interviews, they always leave 5-10 mins for you to ask questions so have a few up your sleave - and ask intelligent questions so they know you're genuinely intereste din workng there and not something you cna find out on their websote), socialise with other applicants and just be yourself!
Sorry I dont know much about mid tier ones but for Big4 the pay for full time work/part time study is 30k-31k pa and that excludes text book allowances etc. And you get heaps of annual/study/exam leave! And all the Big4 offices are gorgeous! EY was so posh and KPMG's views were amazing!
Good luck and woah that was a long post!