So what I gather from the replies..
- Don't work at Coles or Chemists or anything to look for a part-time job
- Use your work experience wisely
Also your input on your work experience... was very much appreciated 
Even though the majority of you had bad experiences lol
I think you're quite confused about the purpose of work experience.
First of all, you're not allowed to do work experience in the summer (I tried to do that myself). Even though it doesn't make much sense, your school needs to be open so that your placement has someone to contact in the case of an emergency (well this is what my careers advisor told me anyway).
Secondly, you should never use work experience in order to try out for a part-time job. Not only does your school facilitate the possibility, but the government subsidises your week off school in order to allow you to properly explore your future and organising it at a retail store (unless you intend to work at one for the rest of your life) would be a huge waste on everyone's time, money and effort. Some students at my school did something similar where they organised themselves full-time work at their existing part-time employer and the ones who somewhat care for their education really regret not taking the opportunity to experience a particular career path. Also, people were detained at my school if they didn't take their work experience seriously, which might also happen at your school too. If you're considering getting a part-time job after school, many workplaces are happy to allow you to try things out after your interview before you commit to anything (I know my employer did), so there is no need to use a work experience week to do this.
It's good you're getting organised early - back in Year 10 I was considering a career in journalism (yeah, I thought I was good at English - I must have been living in a bubble lol) and I found getting a placement really tough and this was six months in advance!
Looking for placements isn't really difficult and don't be afraid to try something a little bit different. Your careers advisor is there to help you too and one thing you'll need to learn heading into VCE is how to use yours to your advantage. If you're going to try at larger organisations you might find they have a work experience webpage detailing the application process - otherwise grabbing out the phonebook and giving some places a ring is equally effective too.
Let me know when you start to get this process rolling because there's a lot of great things that can come out of the experience. For example, I still have contacts at Network Ten and I know one journalist working there would love to see me return. It really does have the potential to make one's career if you do things right. 
EDIT: @ El2012: The standard payment for work experience is $5 per day in order to cover your transportation/lunch costs (I know it doesn't but go tell the government that -.-). Definitely do not question the amount you are being paid - it is about the experience, not about your income.
Damn so I'm not allowed to do it in Summer.. makes my holidays even more boring..
And I want to have a decent idea now so there's not a massive line for the careers advisor since it'l be a new school and all.. I'll ask my current school about it and see what they tell me but thank you for answering the majority of my questions. Changed my perspective on work experience and I'm looking forward to it now. Plus it was good to hear that you enjoyed your experience 
You can do multiple placements - I did two, one with a barrister situated about 20m from the Supreme, Magistrate and County Courts and another one at the Melbourne Football Club. Both fantastic.
Don't do the part-time job thing. Not only is it an awful cliche, it's just a waste. There are better ways to get a job.
About to post when yours came up.. but YOU CAN DO MULTIPLE PLACEMENTS!? Sounds awesome but I don't want to spend too much time away from school unless they have it in the school holidays excluding the Summer holidays then it might work 
I did three work experiences and you are allowed to do them in your term holidays (as long as the school office is open). Otherwise, if you know someone well enough, you could definitely organise an 'off-the-books' placement during this time.
If you are starting to look, here are some other things you might want to know:
- If you're calling up a company, ask for their Human Resources Manager (if they have one)
- Always call up yourself - nothing sounds worse to the organisation than mummy or daddy organising a placement for their child
- Get your resume up to scratch
- Call in a week before your placement to confirm that you are actually going
- If you're sick, call in early (and do not call the school - do it directly to your employer)
- After your week is finished, send a thank you letter to your employer. If it was a positive experience, express your interest in potentially working in that field of area in the future (they will hold onto your details then)
Hopefully I don't need to remind you of how to behave in these instances.

I know it seems over-the-top, but if you're going to enquire in industries that are particularly competitive, these little things put you ahead of the pack. Believe it or not, but journalism is extremely difficult to get into. Work experience and internship placements are scarce and often your employment is based on your appearance or your contacts (one of the reasons I don't want to do it anymore - everything behind the scenes was so fake) and the university you attend really matters (if you don't manage the 94+ ATAR to get into RMIT, you can kiss your chances at a rewarding career goodbye). I got rejected a lot and it was these little things that made me stand out in Network Ten's applicant selection process so I can truly vouch that the small measures above do help a lot.