Sydney is a beautiful place and though I spent almost 2 weeks there, I feel that that was more than enough time. Significantly more than enough. Personally I would recommend between 4-6 days there maximum so here is a 5 day itinerary that you could use.
Walk around the city. It is a fairly small city and you will be able to see many attractions. If you stay near Darling Harbour you could start with that, then walk towards the Chinese Garden of Friendship & ICC. There are benches that are shaped like upright sun beds that you can relax on in front of the water fountains.
For lunch, you can visit the food court inside the Darling Harbour shopping centre, it is very reasonable with options varying from western fast food to Asian fusion.
In the afternoon, you could walk to the Royal Botanic Gardens and as you come out, you can visit Lady Macquarie’s Chair, a viewpoint where you’ll get a great view of the Sydney Opera House and Harbour Bridge.
If you follow the path around, then you’ll walk right up to the Opera House and can get some great pictures. There’s usually a cruise ship there too.
Bondi Beach! You can get the bus or train using an Opal Card (pre paid travel card similar to London’s Oyster Card). It is about an hours bus ride from Sydney City Centre in traffic.
When on Bondi, make sure you swim between the red & yellow flags as that is where the lifeguards have seemed it safe & will patrol.
If you prefer the pool to the sea then there is also an outdoor pool called Bondi Iceberg Pools which you can pay to swim in. You will have a view of the beach whilst you swim.
If you want to add some walking to your day, you can do all or part of the Bondi to Coogee walk which is a coastal walk to different beaches. It isn’t a hard walk but might hurt your ankles/knees if you have an injury and are wearing flip flops. We stopped at Clovelly Beach for a BYO (bring your own) BBQ food & then a snorkel and relax on the smaller, less crowded beach.
Take a walk around Hyde Park and have a picnic.
You could go on a Sydney Harbour Cruise. Book into a boat and enjoy a leisurely boat ride around the harbour and then the boat will stop somewhere for a little while so that you can have a little swim.
Ferry to Manly. You can get the fast ferry which takes 20 minutes for $9.10 (one way) or you can get the normal ferry which takes 30 minutes for $1 (one way).
In Manly, there are little shops and a beautiful beach too.
Visit Sydney Tower, you can have an all you can eat buffet whilst revolving giving you a 360 degree view of Sydney. I went for sunset but you can visit during the day too.
What is your favourite thing to do in Sydney?