The best way to get around is by renting your own car. Magnetic Island is known for their “Barbie cars” which are tiny pink cars that you can rent, and use to drive all around the island exploring all the different bays. This is the most efficient way to ensure you get to see everything in just one day. The price is between 70-80 AUD for a day.
If you’re not comfortable with driving, don’t worry. The public transportation on the island is pretty good, with buses leaving around every 40 minutes. The buses are organized so that they take you to the most popular spots on the island, and ensure you get to see everything that is worth seeing. This is also a very cheap option. You can buy day-tickets, and hop-on hop-off wherever you need to.
Lastly you can rent bikes, and even walk. The island isn’t too big, reaching maybe 10 km from the one end to the other. So you can pretty much bike around the island if you want to.