A Visa Run is the most likely reason people visit Ranong. To start the process, catch a songthaew (#3 and #4) from the market (there is a bank nearby and it open 7 days a week from 09:00 to15:00 and will give you "new" USD10 bill at bank rate) on the main road in Town Center, or take songthaew #6 (South bound) on Route 4 right next to bus terminal. It costs 15 baht (Jan 2014, some drivers "forget" to give you change if you give your driver a 20 baht bill) to get to Saphan Pla, the fishing port providing the link to Kawthoung (aka Victoria Point), a fishing town in Myanmar. Most songthaews end up here eventually, though some follow a longer route than others. You get off when your driver pay a toll fee near a big fuel station on your right. The pier and immigration office is right behind the fuel station. A bank (Mon-Fri 08:30-15:30) is on the other of the main road. Your first stop is to go the immigration office where you must formally exit Thailand. Get your passport stamped and then head for the pier.
It is likely you will be offered a boat by touts. A longtail boat should cost around 300 baht (return), whether you're on your own or in a group. The price you pay for a boat should be negotiated before you get in: there are reports of tourists being charged up to 1,000 baht. If you want to be stubborn you can take one of the longtail boats with all the Burmese people in it and can get a trip one-way for 50THB (circa 2012). They will try to say no at first but make sure you bring two 50THB bills (one for the ride there, one for the ride back) and do not ask for change or they will try to keep the change. There is also a big boat which is used by more organised visa runs, and a small-scale trip via longtail usually coordinated by a white haired chap in a gold coloured pickup who hangs around the bus station. Longtails are faster and fewer people mean less waiting time at the various immigration points. The big boat is slower and takes longer because of the number of passports to be checked, but can work out cheaper.
Entry into Myanmar costs US$10, and notes should be in good condition, especially with no writing on them. Local touts sell US dollar notes but at bad exchange rates. There is a bank in front of the pier, you can exchange your money there with normal exchange rates. On weekends the Myanmar authorities also require photocopies of your passport done by a small shop at the immigration office for 10 baht.
The boat will first go to a Thai Immigration checkpoint, and the driver will take your passport to be inspected, then to a Myanmar Immigration checkpoint a few km further on. For some reason they don't need to see your passport there. When you arrive in Kawthoung there will be plenty of touts offering cheap whiskey/cigarettes/guided tours. You must first enter the country by going to the immigration office to the left as you exit the short pier to pay US$10 and tell the officials, who speak English, that you're a day-tripper. Two weeks visa are sold, which could be useful as Kawthoung could be well worth a few days. If you're just staying the day, Myanmar immigration will stamp you in and out in one go so you won't have to return on your way out.
You'll probably be offered counterfeit Valium and Viagra by touts, and steered towards shops selling cheap alcohol and cigarettes. There is a limit on what can be brought back legally, and the boat may be checked on the return journey. You'll also be offered a one-hour sight-seeing trip on a moped from the touts. At the end of the trip you may be told that the price you agreed was for the moped only and that you need to pay further for the guide himself. It's well worth spending some time in the village even if you're just doing the day trip.
After the boat trip back you must return to the Thai immigration office to formally re-enter the country.
Extract from: https://wikitravel.org/en/Ranong