Foreigners planning to stay in Bangkok over 90 days (on selected non-immigrant visa) must notify immigration of their intention to stay (as here). This is generally for working or spouse VISAs.
There are 3 options for this.
1. Bangkok Immigration Office
The Bangkok Immigration Office is far from the central Bangkok areas. A taxi directly there is possible but can be more conveniently reached using the MRT (Chatuchak) or BTS (Mo Chit) before taxiing. From Mo Chit / Chatuchak a taxi fare is roughly 100 baht to find the Bangkok Immigration Office.
Taxis may drop you at the front Government Complex on the main road (consular building). Be sure to go to Chaeng Wattana Soi 7 otherwise a 30 baht motorbike taxi or lengthy walk is necessary to find the Bangkok Immigration Office building (pictured above with lake front). The image below (1) show directions from main road.
Best to arrive early. Office hours are between 08.30 – 16.30. There is a 1 hour break between 12 noon – 1pm. Full times list in image below (2). To save time fill out the TM47 forms for 90 day renewal before arrival.
Full address: Immigration Division 1 Office, Chalermprakiat Government Complex, Chaengwattana Rd (soi 7), Laksi, Bangkok.
2. By Mail
The lazy option. Send at least 15 days before renewal date to the Bangkok Immigration Office. Stuff envelope with documents below and send to below address. Use registered mail and provide a return address. If no return address use the above option.
You will need to send the following documents:
90 DAYS REGISTRATION,
IMMIGRATION DIVISION 1
Chalermprakiat Government Complex
120 MOO 3, CHAENGWATTANA ROAD,SOI 7,
LAKSI, BANGKOK. 10210
3. Border Crossings
My preferred option but certainly not the cheapest or most practical. You only have to cross and re-enter at the border to be stamped by immigration. This can be done at land borders or airports. If using this option I suggest making the most of it and enjoy a trip to Hong Kong, Singapore etc. The most exciting of the 3 options and avoids the tedious trip to Bangkok Immigration Office.