If you are going to work in Thailand then you can apply for a work permit while holding a number of Thai visas. Most people work in Thailand after obtaining a Thai Business Visa to apply for the visa. This visa has to be applied for at a Thai embassy who will issue the visa for you. If you are going to teach in Thailand then you need to speak to a lawyer as to all the documents needed as these do change.
If it is not for teaching then the work permit process is much easier. You can also apply for a work permit in Thailand while you have a retirement visa or a marriage visa. Note that if you cancel you work permit later then the visa you applied with will also be canceled and you need to start the process again. Example – You have a 12 month extended visa and apply for a work permit with this visa. 3 months down the line you leave your employ and the work permit is canceled. Now your 12 month visa that still would have had 9 months left is also canceled.
You need to show the following documents: Teachers license, Letter from school and their registration, you resume and also your qualifications which you might have. Some embassies also want a copy of your police clearance certificate.
You need your resume and the business VAT and Tax registration from the business. You also need a letter of invite from the business to secure the visa.
For the Media:
You need your resume and 3 published articles. You also need the VAT and tax registration for the business who is going to employ you. You also need a letter of invite fro the company.
If you are in Thailand then the most common Thai embassies tend to be the Thai Embassy in Laos, the Thai Embassy in Cambodia as well as the Thai Embassy in KL and the Thai Embassy in Singapore. See them for more information and advice as each has their own system. The Thai Embassy in Penang is very difficult and extremely strict.