First thing is to decide what kind of business you want to open. Once that is decided everything else is easy and just a matter of logistics.
We assume you know who your typical customers will be.
We assume how many employees you will need.
We assume you’ve figured out how you will market your business to those customers.
We assume you know how much money you will need to cover expenses for staffing.
All the above is 1000 times harder than opening the business itself.
Find a local partner in Thailand and ask us to register the company and optionally prepare the paperwork for your work permit and visa. Those parts are not hard.