The Thai language is a unique language, only spoken in Thailand and not closely related to any other language with the exception of Lao. It has some unique grammar, 5 tones, and a very unique alphabet, making it a very difficult language to learn for Westerners. What gets me are the tones. You can say they same sound in 5 different tones, and they can mean 5 completely different things. And tones are subtle to us Westerners. A subtle raising of the tone to emphasize a point in English can alter the entire meaning of a sentence in Thai.
Before you go this summer, do yourself a favor and get a guidebook. And peruse it before you go. They have lots of suggestions and recommendations, and if they are from a good guidebook, they are typically spot on. And the sections on culture, history, arts, etiquette, geography, weather, etc. are invaluable.
There are a ton of guidebooks, from a variety of publishers, including Fodors, Rough Guide, Moon, and a host of smaller publishers. I am partial to Lonely Planet. The audience that they write for seems to be spot on with the type of travel I enjoy (going on a budget, exploring on our own, independent of tourguides and tour companies, going to out-of-the-way places where typical tourists are scarce, using local transportation, etc). Fodors seems to be targeting a more upscale traveller, and Rough Guides seems to target the backpacker crowd. Lonely Planet seems to be in a nice medium. (By the way, these websites have a LOT of good information for travellers, so they are definitely worth perusing.)