By road
Hitchhiking works pretty great in Montenegro. See Hitchwiki for more details.
By car
As there is no real highway in Montenegro; most roads are two-lane only, with frequent addition of a third overtaking lane, and generally are not up to European standards. Most roads are curvy and mountainous, so speeds over 80 km/h 50 mph are rarely legal, and rarely safe.
The speed limit is 80 km/h on the open road, unless signs specify otherwise. The speed limit inside the cities is 50 km/h.
The use of safety belts and headlights during the day is compulsory, and the use of cellphones while driving is prohibited. Signposts used in Montenegro are almost identical to those used in EU countries.
Local drivers tend to drive fast, and to get involved into dangerous overtakings. Traffic jams are common during the peak of the summer season. Pedestrians are notorious for jaywalking in every Montenegrin city.
Drivers tend to be extremely vocal, so don't take it personally if a driver yells at you.