• BBC Learning English: “sh” and “ch” sounds:

(Thai) Learn the sh and ch sounds - improve your pronunciation with English on the Street

• “l” and “r” sounds:

https://www.youtube.com/watch?v=7t90bDRROtg

• 10 common pronunciation errors:

10 English Pronunciation Errors by Thai Speakers

• 8 week course (free, self-study)

Learn English Pronunciation: Free Online Accent Training for Learners from Southeast Asia

• General tips, partially in Thai:

ChadVer Online : English Pronunciation Course for Thais