Purchase a Thai book for beginners. Books enable you to practice the phonetic spoken language and give you something that you can carry around for reference when you are in Thailand. Many guidebooks to Thailand also contain useful Thai phrases.
Purchase a "learn Thai" CD. Listening to and repeating after a Thai speaking the languages helps you get the correct pronunciation. You are introduced to the Thai language on a gradual basis, starting with greetings and working your way through the more complex phrases.
Purchase a language software program. A number of software packages use pictures, audio and video to help you learn Thai. If you are not sure whether reading or listening will help you learn more effectively, combine all methods so that you can decide how you learn best.
Sign up for Thai lessons at a language school if possible.
Talk to Thai people. A very effective way of learning a language is to practice speaking it with native speakers. The more you try to speak the basic phrases the more proficient you will get at them. Try to avoid speaking English when at all possible when practicing Thai with Thai people.