Marriage registration in Thailand starts with affirmations from your embassy in Thailand confirming not only your citizenship but that you are single and therefore being able to get married in Thailand.
This affirmation is an overnight process. Obtain the format from your embassy and complete it at home. Then take the affirmation back to the embassy and have them sign off on the affirmation
Marriage registration in Thailand can become a drawn out affair. You would also need to produce your original divorce decree or the death certificate of your late spouse if he or she has passed away or if you are divorced.