Like most Greek islands, Samos is at its busiest in the summer months. The rest of the year, it is very quiet, with little traffic on the roads. In the summer, things get busier. You'll find parking lots close to all the beaches. If you're visiting in July or August, be sure to get up early for a day at the beach — it'll be hard to find a parking spot if you arrive at midday.
Pythagorio, like most towns on Samos, was not made for cars. The streets are very narrow, particularly in the old town. It's a good idea to park your car by the harbor and explore the village on foot. As it's a small village, this won't take long.
There are no highways on the island of Samos. Instead, you'll be driving on mountain roads, which often have extreme curves and bends. There is one main road that runs all around the island in a loop. You'll soon become familiar with it, as you'll probably be using it to get from Pythagorio to other destinations. This road is in good condition and is the widest on the island; other roads are often very narrow, making passing difficult.
When you turn off the main road, conditions can change abruptly. You'll often find dirt or gravel roads. A 4WD is not necessary, but you'll need to drive slowly as you make your way along these access roads that lead to beaches or other places of interest.
Driving in the interior of the mountain, you're very likely to come across animals. Stray dogs are a sad but common sight on rural Greek roads. Take care, as they may be nervy and might suddenly bolt into the road. Other hazards include herds of goats. If you find yourself stuck behind a group of these creatures, relax. They tend to act as if they own the road and won't respond well to honking. If it's not possible to drive carefully around them, you'll just have to wait for them to move on.
You'll also need to watch out for motorbikes and mopeds, a common sight on winding mountain roads. These are very popular with young Greeks, who may ride them recklessly around the island. Remain calm and avoid driving at night.
Make sure you are carrying cash to pay for gas, as gas stations sometimes do not have facilities for card payments. You will also need cash for parking meters, although you'll usually be able to find free parking instead.