Suva has one of the very few ports in the Fiji islands where even such giant ships like the Dawn Princess with around 2000 passangers and 800 crewmembers onboard will be able to dock right in the citycentre.
That fact will save you a lot of time, when you want to explore the city. Once that you have left the ship there are no further controls by the local authorities and a market-hall and lots of shops will be in walking-distance of just some meters from the ship.
So you dont necessarily have to book any of the - mostly quite expensive - tours through the ships tour-office.
From the cruiseport you can easily walk to all sights of interest that you will see and read about in this page. From the port you simply take the Thomson Street to the right - seen from the ship - and after some hundreds of meters that street will be called Victoria Parade, which is the main street of Suva with many of the most beautiful and many of the buildings that are of interest for the tourists.
Calculate about 2-4 hours when you want to see all of these places. The Fiji-museum and the presidential palace are about 2km to walk from the ship.
Just a small warning. The taxi's in Suva are generally quite old, which is no major drama. Keep in mind though that most taxi's do not have meters. Taxi drivers will often try to overcharge you for a fare from the airport into Suva. I recommend negotiating a price before leaving the airport. The usual fare is around FJD$30.