The wai (as mentioned above) is the traditional form of greeting, given by the person of lower status to the person of higher status.
Thais generally use first rather than surnames, with the honorific title Khun before the name. Khun is an all- purpose form of address that is appropriate for both men and women
In general, wait for your host and hostess to introduce you to the other guests. This allows everyone to understand your status relative to their own, and thus know who performs the wai and how low the head should be bowed.