Oliva is at southernmost tip of the Costa Azahar 'Blossom Coast' and is situated between two of the major airports, Alicante which is about an hour and a half away and Valencia about an hour away.
There are coaches from Alicante to Oliva, but you do need change at Benidorm and then get a taxi from Oliva. Valencia is easier as there are regular metro and train services to Gandia, and then a taxi to Oliva Nova.
I do however, advise car hire though as, although there are shops, bars and restaurants within walking distance, Oliva town is 4 kilometres away.
Oliva is just off the AP7, the main motorway that runs the length of Spain's eastern coast.