Avoid tips and tricks from people who have lived in Thailand for 2-3 years. Their experience is too partial and what they find memorable is not very useful. And their sad attempt at providing a glossary or phrasebook is a waste of time (the tones are as important as the sounds, if you don't get the tones right you are saying the wrong thing). That said, here are some things that cannot be overestimated:
This is a different culture from the west. Very different, in many ways. Learn about culture shock, you will have it here. Expectations are regularly violated, both for the traveler and for the local people inside Thailand who interact with travelers. Yes, there are many Thai people who are used to foreigners and are more-or-less bi-cultural, but this isn't the case for the vast majority of Thai people.
Thailand has an immense variety of places, from city to countryside, beaches to mountaintops, high society (hi-so) super-expensive to the least expensive and least sophisticated, in terms of food, lodging, entertainment, etc. Find where you are most comfortable in the range of cultural and geographical diversity, then explore up and down a little as well.
Smile more. Get angry less. Be more patient. Don't touch monks. Careful with your feet. Speak more softly. Calm down. Open your mind and your heart. But be careful with the wallet, there are some bad people as well.