There are many ways to get to Rovinj.
Here are some recommendations:
The closest airports are:
There are some cheap airlines (EasyJet, Flyglobespan, German Wings, Ryan Air, ScandJet, TUIFly, Wizzair) flying to these town. There is a great page that might help you find the right flight for you!
For all salseros coming from Italy or passing through Italy, you might want to look at a ferry line from Venice to Rovinj. Please look at this link for more information:
Coming by car? Having your own transportation? Look at some of the rout planning sites:
The closest train stations are in Rijeka and Pula. You can take the bus from there to Rovinj.
For some general regulations in Croatia, please look at the following pages:
Also, a site of Croatian Tourist Board can help you find some more info on travel to Croatia.