Ride around the Island

Phu Quoc is very well suited to motorcycle trips. Be warned that the roads are very infrequently shaded, so wear a hat and drink a lot of water to keep sunstroke at bay.
Southern loop
Head south from Duong Dong till you reach the junction with the road to Ham Ninh -- take the left turn and ride onwards to Suoi Tranh waterfall. The waterfall isn't sign posted, but just keep an eye out for the massive concrete gates on your left -- that's the entrance. There's a small charge for leaving your motorbike. The falls are more of a river running over rocks than anything else, but it's nevertheless a pleasant and cool environment.
Once you're done there, continue on the road towards Ham Ninh, but when you reach a main right, take it, heading south to Bai Sao beach. Along the way you'll come to a sealed left which runs down to Bai Vong beach, so if you want to see Bai Vong as well, take that. Otherwise, continue southwards to Bai Sao. The turnoff isn't clearly marked, but it's at the top of a rise and there's a bunch of beer and cafe signs -- that's where you want to go.

Follow the sometimes bumpy dirt road down to Bai Sao beach and decamp for lunch and a good deal of frolicking. Once done, get back onto the main road and head south till you reach a sealed road running off to the right -- take the right -- if you continue straight ahead you'll end up in An Thoi.

Follow the road around to the right and you'll end up running up the length of Long beach till you hit Duong Dong. Stop as many times as possible for a swim and don't forget to swing by the pearl farm.

Western loop

This is one of the prettiest loops. Head north from Duong Dong -- it's a little confusing as the signposting isn't great, but keep bearing left and following the signs to Mango Bay -- eventually you'll end up on the right road. Following this road takes you to the turnoffs to Mango Bay and Bo Resort -- both of which are worth dropping by for a coffee or snack, accompanied by a swim.
Continue north, along Vung Bau Beach and at the northern point you'll reach a great viewpoint looking back over the beach and down the coast. Continue north and you'll reach a seafood restaurant with good views across to Cambodia -- the frontier is a mere five kilometres from here.

After lunch continue eastwards till you reach a T-junction and take the right. This road takes you back to Duong Dong through some pleasing stretches of forest.

Eastern loop

Head south from Duong Dong and take the turn east as per the southern loop, but instead of turning south after the waterfall, continue east till you reach Ham Ninh.
Ham Ninh is a small fishing village with a couple of excellent seafood restaurants. The food is outstanding -- just be sure to confirm the prices before eating anything. Once you're well fed, head north along the coastal road. Lots of deserted scenery up here till you reach a bunch of rather scenic islets just off the coast.

After that the road tends southwestward and eventually hooks up with the main road back to Duong Dong.