By bus
There are scheduled shuttle buses to Lovina from most major tourist destinations in Bali. These are reliable and cheap. Check the advertised services locally and book one day in advance. Perama (http://peramatour.com) has an island-wide network and a local office in Lovina at Anturan.
Bemos servicing Singaraja depart from Ubung terminal in Denpasar.
By car
There are several routes used to access the northern region of Bali, some much more often used than others.
From the south. The main road through the highlands comes down the northern face of the central mountain range and continues into Singaraja. This is a picturesque drive. Driving time from Bedugul in Central Bali about 1 hour, from Ubud about 2 hours and from the main tourist destinations in South Bali, about 3 hours.
An alternative and even more scenic route involves turning west at Lake Buyan in Bedugul and heading through the village of Munduk and onto Seririt on the north coast. From there it is about a 20 minute drive eastwards to Lovina. This journey can take as long as you want it to. Take your time and really enjoy the magnificent scenery.
From the east. The east coast route into north Bali goes through some very barren terrain with stark views of Mount Agung across flat gravel plains. From Amed the drive to Singaraja will take 1 hour to 90 minutes.
There is a less used route which comes in from the highlands at Kintamani hitting the north coast road at Kubututambahan, just east of Singaraja.
From the west. The road follows the coast from Pemuteran in West Bali to Lovina through some lovely, laid-back coastal villages. Driving time about 1 hour.