In principle, you could just fly into the airport, go to a rental desk, hire a car and go. But to be sure you'll get the car you want at the price you want, you should reserve your car in advance. A good way to do this is through one of the world leading companies below or a TTP recommended travel agencies.
Rental Cars in Izmir
Distances & Travel Times from the Airport:
Ankara: 618 km (384 miles) E, 6 hours
Ayvalık: 158 km (98 miles) N, 2-1/2 hours
Bergama (Pergamum): 118 km (73 miles) N, 1-3/4 hours
Bodrum: 232 km (144 miles) S, 4 hours
Çanakkale (Dardanelles): 358 km (222 miles) N, 5 hours
Istanbul: 628 km (390 miles) N, 8 hours
Izmir: 18 km (11 miles) N, 35 minutes
Marmaris: 302 km (189 miles) S, 4.5 hours
Pamukkale: 252 km (157 miles) E, 4 hours
Selçuk (Ephesus): 62 km (39 miles) S, 1-1/4 hours
Here are distances and travel times from Izmir.