Originally, the Thai language was very similar to Chinese. I've been studying Mandarin Chinese for a year on and off and found some similarities and differences which I would like to share today.
Both are SVO
They consist primarily of monosyllabic words, use similar word and sentence construction patterns, and they do not conjugate either verbs or nouns (their grammar is quite simple).
Some Thai words preserve the Old Chinese pronunciations.
Some Thai volcabulary has Chinese origin (after all Thai originated as sino tribe of ancient China), most however are Indianized nothing similar. For example, the Old Chinese pronunciation of the word 交 (jiāo) "to mix" is *kraw which is almost the same as “เคลา” or “เคล้า” (klaw) as in “คลุกเคล้า” (klùgkláw, “to mix together”) in Thai.
Tone are pretty similar.
They are both tonal languages, but they are not in the same language family. Thai has 5 tones. Mandarin has 4 tones. And they use different writing systems. Though Thai and Chinese comes from the Sino-Tibetan group, the languages are still drastically different.
Short and long vowels
Both languages have short and long vowels e.g. sawaddii Hello! or Good Day! ("sa-wad" are short vowels but "dii" is long vowel.)
Thai and Chinese grammar are so much easier than Japanese and Korean but pronunciation and writing systems are harder! I found that my Chinese-speaking students can pick up Thai easily and at the same time Thais can also study Mandarin faster than studying Japanese or Korean languages.
If you did minimal mistakes, it's still understandable.
Fortunately, word orders of Thai and Chinese are pretty flexible. Even you did minimal mistakes, putting things here and there or pretty much clutter at the start, native speakers can guess what you're trying to say. Plus you don't have to worry about conjugation.
As a multilinguist myself, I personally think that there are many similar words in Thai and Mandarin. Anyway, for learning I like watching video courses and work with native speakers 1-on-1 on Skype. For studying tonal languages, these are faster and more accurate methods than doing self-study.