I suggest you work to your strengths. If you are taking "just photos" I suggest you demonstrate conceptual strength, or display them in an intresting, unique way.
And of course, you need to show 12 months of work, ie. 24 photos submitted on their own would probably not get you a band 6 mark, unless they were really, really good.
Also, if you are doing photography, i sugest you take heaps of photos. Seriously, my BOW was submitted as sculpture/photography and it included 144 photos, but i would probably have taken about 400 all up, maybe more.
But yeah, that's my advice.
Ohh, and think about every time you shoot, don't just point and click, seriously think about what you are trying to do with every shot.