Montenegro has a relatively good bus network that connects all the cities. It is also well connected with neighboring countries: Croatia, Serbia, Bosnia and Albania.
However, Montenegro is a small country so certain lines are not very regular and their availability varies depending on the time of the year. Depending on your route, you might end up in old and poorly equipped bus which might reflect on the quality of your trip.
If you need a transfer between two places in Montenegro, much better option is to book a private transfer. It is an affordable option especially if you're travelling as a family or a group. Private transfers offer door-to-door service which saves your valuable vacation time.
If you're looking for a short-relation transport within a city, we'd recommend taking a local Taxi. They are usually quite affordable but do check in advance with the driver about the approximate cost of the journey. Cities in Montenegro are relatively small so they do not have very good bus infrastructure.
If you need an airport transfer, by far the best option would be to book an airport transfer online. There are no regular bus shuttles from Montenegro airports, and bus shuttle at Dubrovnik airport goes only directly to Dubrovnik centre. There are taxis waiting at the airport, but they are typically much more expensive if you book them on the spot. Also, do note that taxi drivers at Dubrovnik airport can only take you to Montenegro border and no further due to law restrictions.