Because of the large size of Crete the best way to visit at least part of it is by car. There is also a good public bus service but connections to smaller places are not very frequent.
Most places with a tourist population will have car rental offices.
It is generally more expensive to use large car rental operators such as Hertz and Avis. There are many excellent local companies that will probably give you better prices and service.
If you plan to rent a vehicle once you are on Crete shop around as prices
can vary considerably. Outside of the July and August months and especially
if you want to hire for a week or more you can get excellent
deals. When comparing prices between different car rental agencies,
make sure that you are comparing prices for the same vehicle class. length
of rental and range of services (in general - but by no means always - unlimited
mileage, comprehensive insurance and breakdown recovery). Check the mechanical
condition of the fleet - this is especially important if you want to rent
a two-wheeler. Children's safety seats are provided when needed.
When offered a helmet for a two-wheeler make sure that it fits you and wear it or you risk being fined by the police.
A popular option in some of the larger resorts of East Crete are quads. These are not very safe to be driven on roads and there have been many accidents.
If you are considering driving on Crete have a look at this page on driving customs.