Check some basics about your employer. This is the most important thing! Should have a minimum of 2 Million Baht in registered capital per work permit in the company. The best option is that the capital is paid up, not just registered on paper. Minimum 4 employees per work permit in the company.
Step 2: Get a NON-B visa to enter Thailand. You must secure a non-immigrant visa B to enter Thailand. This visa can only be obtained in your home country or outside Thailand. You have to prepare it before you come to Thailand.
If you are already in Thailand, you have to travel out and apply for a Non-Immigrant Visa "B" outside of Thailand. You have to go for a visa run! You will need the company papers and a letter from the company in order to apply for a Non-B from the Thai consulate/embassy. Once, you are already in Thailand you may now apply for work permit.
Step 3: Check, check and double-check! Recheck all documents needed. Your Thai employer will say that everything is in order, but may not be!! So Double check! Apply for the work permit at the Thai Labour Department for the province the Company is located in. Most people get refused because they forgot to include a map in Thai showing the location of the company. Some other people get refused because they were not wearing a necktie in the photo. The Photos of the office must also show clearly the Company name and address. Double check the requirements! The application will take 2-3 weeks.
Step 4: Pick up your work permit. You will need to pick up your blue work permit book in person at the Labour Department. The permit will be valid as long as your visa is valid, as in your passport.
Pick up five extra forms for "Extension of Work Permit " (you will need a few of these later!)
NOTE: Be sure that you do not overstay or travel out of the country without a Re-entry Permit, because then your visa will be invalid and you will have to start the entire process over again.
Apply for a One Year Extension of stay at the immigration. You will need some extra documents, copies of your work permit and you will also need a set of papers similar to the one you submitted to the Labour Department. Immigration will first extend your NON-B only 30 days. If they do extend, then you are OK for now. Make sure you make another Re-entry Permit if you plan to travel, as the previous re-entry permit is now invalid.
Step 6: Update your work permit book ! Go back to Labour Department and extend the work permit to be stamped up to the same day as your visa extension. Your work permit book shall now have the same expiry date as your visa.
Step 7: Check with Immigration again. At least three (3) working days before the visa extension expires, you have to visit Immigration again, and check your status. They will probably stamp you with another 30 days extension. And, needless to say, make another new Re-entry Permit if you plan to travel, as the previous one is now invalid.
Step 8: Update the blue Work Permit book again. Go back to Labour Department again and update the Work Permit (as Step 6).
(You have to come back after 30 days and you will get another extension of 30 days. Your application is under consideration, says the stamp in the passport.)
Step 9: One Year Visa from Immigration.
This procedure can go on for several months, until you get the one year extension. Every extension requires a new Re-entry Permit if you will be travelling outside of Thailand. That extension will be valid until 1 year after the first day you entered Thailand with your new NON-B visa.
NOTE: The very same day that you receive your one-year extension, you should apply for a Multiple Re-entry Permit, so you will be able to travel freely in and out of the country without losing your visa.
NOTE: If you forget to obtain a re-entry permit and travel out of Thailand, you have to start from Step 1 again. Every new extension like this requires a new Re-entry Permit (and nobody will inform you of that!)