I'm a sociology but it's a little similar.
For a research proposal, you want to identify a narrow topic of your research. What in criminology do you want to study at a PhD level? Before you apply, you should know what you want to study, AND determine whether there are academics at your university that can supervise that topic. Criminology (like any discipline) has a range of topics, so just because it's offered, doesn't mean there is someone who can supervise you unless they have similar interests within criminology.
A Good Research Proposal
-Identify your research topic
-Do a mini-literature review, find out what has and hasn't been said
-Develop a research question, what is it you want to know?
-Develop your methods,i.e. will this be case study based, content analysis, survey, interviews, focus groups?
-Write it all out in a neat and formulaic pattern
Keep in mind that your proposal won't be what your final product is, this will change over the course of your study. You said your background is psychology, so you might want to find out what you might need to 'catch up on' if you haven't got much experience around criminology.
I'm not sure how it works at UNSW Australia but at University of Melbourne and Monash University, my scholarship application was not based on how great the research proposal was, I don't think that was even considered. Rather, they were around past research experience, past access to funding, grades, conference experience, teaching experience, field placement/hands on research experience, previous publications etc. I would get in touch with the postgraduate administrator who can give you a better idea of what your application will need to stand out.
