First, try to master listening comprehension and reading comprehension skills at intermediate level. With the said two skills you can learn English by yourself from digital media (ebooks, audios, videos and software) produced in English-speaking countries and those offered online for free.
In doing so, you can break away from Thai teaching media and become less dependent on your teachers.
In the old days, Thai students studied grammar and reading comprehension first. With the advent of the Internet and computer assisted language teaching, all the learning priorities must be completely rearranged.