I hope you like roosters waking you up in the morning as they are everywhere.
This is a great place to get married or have your honeymoon.
You can catch the local bus around Rarotonga which is $4 one way or $7 return.
If you want flexibility then hire a motor bike or car.  We hired a small convertible which was a lot of fun.
All the dogs are medium to large size and not on leads.  This is probably due to interbreeding.
It has the best weather, not too hot or cold and is the perfect beach vacation.
You have to get a driver's license from the police station which costs $20 if you want to drive.When riding a bike you don't have to helmet if you go less than 25 kms.
Buy fresh local fruit like bananas and pawpaw (papaya) from roadside stalls.
Take an underwater camera.   You can get disposable ones.  The fish and coral are worth capturing.
Make sure you credit card will work in the automatic teller machines.  Banks on the island are ANZ and Westpac.
Take plenty of sunscreen and a hat.  This applies really to all summer vacation travel destinations but its summer all year round here.
Do a cultural dinner and show.  Most resorts hold them.
Sunday a lot of the shops are closed so don't wait for Sunday to buy those souvenirs.
Take your own snorkel gear.  You can snorkel anytime and anywhere you want then.  Most resorts have them but they won't allow you take them off their property.
Visit the Cultural Markets on a Saturday morning in town.  A lot of the same stuff but it is a good atmosphere with native dances and music as well.

These are my own observations but I encourage you to research the internet for others as well as this will give you a better idea of what to expect and what to do and not do at Rarotonga.  Whatever you do this has to be the best vacation travel destination I have been to.