Landlocked Laos is easily accessed from most of its neighbouring countries, either overland or by flying. Note that visa on arrival is not available at all overland entry points for details and check locally for the most up-to-date information before travel to Laos.
Flying is the easiest way to get into Laos. If you fly through international connections, you most likely will find that it is easier to arrive in Bangkok first. Bangkok connects well with Laos to the airports of Vientiane, Luang Prabang and Pakse. The international airports at Vientiane and Luang Prabang are served by the Lao Airlines and a few others, including Air Asia, China Eastern Airlines, China Southern Airlines, Thai Airways, Bangkok Airways, and Vietnam Airlines. Pakse is the third international airport with flights to/from Siem Reap as well as to/from Ho Chi Minh City.
Vietnam Airline Plane.
From Chiang Mai, and Chiang Rai, you will need to go to the Chiang Khong border crossing in northern Thailand to reach Houay Xay in Laos.
You can also take a train or bus to and from Ubon Thani. From here you can easily make your way to Nong Khai border town. You will have to cross the Friendship Bridge into Vientiane.
If you want to travel into southern Laos, you will have to access Laos via Ubon Ratchathani in Thailand and travel on to the border town of Chong Mek. This border town will bring you to the southern Laos town of Pakse.
It is easy to travel from Bangkok to Vientiane by train, using the daily overnight sleeper train from Bangkok directly to the Thanaleng Train Station in Laos then catch a local bus or tuk-tuk to central Vientiane; or you can use any of Bangkok - Nong Khai trains then making your own way by bus or taxi between Nong Khai and Vientiane.