There are a number of options with regards to weddings in Thailand. Some prefer a traditional Thai wedding while others opt for a Christian wedding or a more secular wedding in Thailand. Very few foreigners go through a traditional Thai weddings with all its traditions however in rural Thailand this is still rather big amongst Thai people themselves. The process begins the day before the wedding and these are the steps.
Thai Weddings
The day before the wedding the monks will arrive at your home and pray and pay homage to the ancestors of the bride. During this process you are only wearing your normal clothing and nothing fancy. 
Usually a total of 9 monks will arrive for this part of the ceremony. They normally sit in a straight row with a bottle of water I front of each of them.
You and your Thai fiancée will site in front of the first monk when the prayers start. He will then take holy thread which looks like wool and wrap it around your head and around the head of your wife while he holds onto the ends of the threads.
There is a bowl of water in front of the two of you and there is normally a candle in the middle of the bowl. They will pray and then when they are done they will return the following day for the full ceremony. The water with the candle in the middle being holy water is put away for the next day.
Traditional Thai Weddings
On the day of your wedding you will have your traditional clothing on for the wedding. They will then take the water from the previous day and sprinkle this over the people who are present. They will again take holy thread and wrap it around you head and around the head of your Thai fiancée and join the two threads together.
Once this is done you both Wai and bow down to the monks. A small tray is now placed before each monk and you will now proceed to place money onto each tray. Since the monks are not allowed to touch the money it gets placed later into envelopes and handed out.
The monks will now leave and the wedding is complete.
There much older traditions in Thailand which are not as common as the one above. What was explained above is what is standard today in Thailand however in the days before modern Thailand they had other ceremonies as well. See this website on other much older Thai wedding traditions which very few people still practice today.
Note that these traditional weddings are not legally binding and that after the ceremony you still have to register your marriage in Thailand. Many who do want to have traditional Thai weddings in Thailand tend to hire a wedding planner in Thailand to do all the arrangements for them. Some of the better known wedding locations are the wedding locations in Phuket as well as the wedding locations in Samui. The scenic backdrop makes for excellent wedding photos.
