The process for getting a teacher's visa in Thailand (non-B) is anything but simple (as of my experiences with Jomtien immigration when I was last there).
First, I needed original proof (housebook or letter from owner) of where I was staying. If the accommodation you are living in is owned by a farang (condo) then you need this letter from the Thai building owner. If you are staying in a hotel/hostel, you need a letter from the owner of that (whether or not they are actually in town/country doesn't matter to the officials, you still needed it). This then had to be authenticated by the city hall.
Secondly, I needed to get my (original) degree certificate sent over from the UK. A photocopy would no longer suffice. It had to be the original certificate.
Waiting for the required documents to arrived was a long and stressful process (what if they got lost in the Thai post?!)
My time on my tourist waiver ran out and I had to take a border run to Cambodia (getting a grilling of who I was, what I was doing in Thailand and why I was there from the stern Thai official at the re-entry border).
I was then told to obtain photographs of myself including one of me "teaching" students, one of me with a Thai colleague and one again stood by the sign for the school name at the front gates (although when I questioned them asking me for pictures of myself teaching without a visa that allows me to teach would have been illegal, they became agitated and said "I tell you already, why you no understand!?"
Of course nobody in Jomtien immigration office spoke English or even explained anything to my Thai partner when I took her with me. It seemed they didn't even know the rules themselves. The request for photographs was way beyond Thai logic and the whole thing would have been hilarious if it wasn't so stressful.
I then waited for more than a couple of weeks for my monumentally incompetent school admin to produce the contract and proof of my employment document.
In the time waiting for this, my 30 days again ran out and I took a weekend trip to Kuala Lumpur, getting another 30 days (and another grilling off Thai immigration at Don Muang).
Thirdly, I had to take this to be legalised and authenticated by the British Embassy of Bangkok.