if you are on a tour.. they will take you to those popular tourist spots..
if you are on free and easy.. just do a street shoot.. tons of people at sydney central taking pics of structures and buildings..
opera house, harbor front or something similar, near the city area. There are lots of parks and beaches.... stay there for one year but several years ago. forget all the names liao
you may buy the day tripper (AUD15 or something) to use bus, train, ferry for one day.. very good price. I usually take ferry, then you can take a lots of pictures on the ferry. The zoo is not bad, also need to take ferry (a very short one) to reach there.
from experience, do not look for photo opportunities
photo opportunities will come and find you, unless you must by all means take record shots of all the popular spots.. which is okay i guess, but not the best and only way to go about it that said, the sydney opera house and the bridge are always popular subjects of photographers, especially at night.