There is a useful post For the ambitious prospective Ph.D student: a guide.
It is written by Rachael Meager, an undergraduate at Melbourne University, about how Australian students can get into top 10 Economics Ph.D programs, largely in the USA.
Much of the advice is also relevant to science and engineering programs, and I suspect beyond Australia.
It is also relevant to Australian students who want to get a high first class honours result so they can get a Ph.D scholarship within Australia, in a leading research group.
I thought it was cute she recommended writing comments on faculty blogs to make them aware of your existence, interest, and sophistication. Lots of economics faculty write blogs.
In the Australian context I would also suggest that students consider limiting or quitting part-time jobs (McDonald's etc.) unless it is a matter of not eating.
The average Australian undergraduate works something like 10-20 hours per week.
It is simply not possible to do this and expect to have a stellar undergraduate performance.
Take out a student loan or cut back on the i-phone, clubbing, car, overseas holidays....
Having a long commute is also something to avoid.
As usual you have to decide what is really important to you and what short-term sacrifices you are willing to make to achieve long term goals.
BTW: the preceding post on the same economics blog by Rohan Pritchford about the state of "tenure" in Australian universities is also a good read.