It was just as scary for us when we started out. I am not sure what type of syllabus you will be using in Thailand, but the chances are that it will have a heavy grammatical component, so make sure you have a decent grammar to be familiar with that area. Use the more experienced teachers in your staffroom- I got a lot of good advice in my early days from experienced colleagues. Be prepared for how you are going to handle cases where you are not sure what the answer is; there are various ways of doing this, but it is better to be prepared.
Be analytical and honest about what works well and what doesn't work in your classes and build on successful strategies.