1. Eat Everything
Try the pad thai, the street food, and the weird stuff you find in the night market. You will never leave Bangkok hungry, but you will leave with a new appreciation for the human digestive system.
2. Learn the Local Slang
Learn to speak Thai, or at least learn the local slang. "Sawat Dee" means "I love you," "Sawat Jai" means "I hate you," and "Sawat Nah" means "I'm just here for the free stuff."
3. Haggling is an Art
Learn to haggle. It's a skill that will serve you well when buying a new motorbike for the price of a used one. Or when buying a used one for the price of a new one. Or when buying a motorbike that's not even a motorbike at all.