Buy a ticket and add your info. Personally, I used an agent. They have an online portal, I just uploaded all of my docs and they told me if I was missing anything; they caught an error that would likely resulted in a denial if I did myself. The cost was $5K Baht for peace of mind; they took care of everything from start to finish and my visa was in my hand in about 5 weeks.
Here is a coupon code for 500 off - I1S94UKY
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