Agreed start as early as possible, even if you don't think you have strong ideas the earlier you start, the more time you have to edit and perfect you major work, and make sure it doesn't eat it into vital time like studying for trials
Secondly, do your bibilography as you go along (it's amazing how the little things add up)
Thirdly, footnote as you go! (I somehow managed to pull an all nighter to perfect my footnotes, even though my actual PIP content was completed.)
Do something that thorougly interests YOU (or that could become interesting to you, because you might end up shedding tears and finding it difficult to overcome barriers during the process and it's much easier to pursue something you personally enjoy rather than merely other people suggesting it is interesting.)
It's okay if your first idea isn't the one you end up with (but don't change your topic to much), because the more you work on it the more you perfect your writing skills and understanding of concepts in the society and culture course.
Don't do subjects such as drugs, sex or popular culture like twilight and emos if you can help it because you're not going to come up as being uniquely ethical or sophisticated. Generally it's better to explore a persistent cultural trait rather than a temporary pop cultural idea.
Finally, try and enjoy it
This is your opprotunity to convey your social and cultural researching skills and what differentiates you from every other society and culture student so convey your unique passions and interests to the marker in a motivating and engaging way
PS feel free to check out marker's notes from previous years as that will tell you general tips from the marking centre about what they like and don't like of the pips they mark. And you can also check the standards package from like 2002 for pips or go to the state library to look at past exemplar examples. Good luck!