Firstly, the basic rules of the road do not apply, such as: using blinkers, those in the roundabout have right-of-way, traffic lanes, direction of flow - all these are optional. Secondly, add scooters to the mix in every available space, pot holes and the odd stray dog. Thirdly, the rental car is stuffed with repaired sails, full propane bottles, grocery shopping, jerry cans of diesel and petrol and likely to explode if rear-ended!
And, yes, Thailand drives on the left.
The trick is to be brave and predictable. Closing your eyes can also be helpful in a Ravenous Bugblatter Beast of Traal kind of way. Edge forward into the roundabout, giving way as needed until you have blocked enough of the road so vehicles start giving way to you. Now you are in, you have to get out! Use the cars in the outside lane to shield you while make the right turn. Watch out for the scooters zipping straight through on your inside. Edge forward once again across the traffic coming in until they stop and you can exit the roundabout.
And do watch for oncoming scooters on the wrong side of the road!