Firstly, safety checks are of utmost importance like your blind spots. You will also realize you look at the opposite flow of traffic when trying to turn which is quite dangerous. You'll get used to it after some time though.
Take note of the car's width and body area. I wasn't used to it on the first day and slightly brushed against a parked bus with my right mirror, nothing really happened though. Use the left lane marker to help keep you in the lane.
Blinking lights means you can go, but look out for other cars - the junction becomes a free for all. Not sure about their right-of-way rules, but just go ahead when you feel it's safe to do so.
You can also turn right on red, sort of like our left turn filter lane, in jeju city/seogwipo city there will usually be a small green light telling you to go, when the main traffic light is red. Or... Just get honked at then you'll know to go haha. Oh and as pinkibee mentioned, the left turns you"ll have to go across the road just like Singapore's right turn, don't go unless the green arrow pops up on the traffic light allowing you to go. I rarely did u-turns so I shan't comment on that.
Other than those points, jeju is a good first place to try left hand driving. Get full excess waiver(I paid 28000 won for 3 days) and if you get some small scratches etc you wouldn't have to pay anything extra. Good luck have fun