Many Thai people always pronounce English words like the way they speak Thai. The factors to this can be considered as prefabricated patterns, the first language transfer or the register. The details about the consonants here can raise your awareness of the differences between some sounds of Thai and English.
The manner and places of articulation are presented here.
http://www.azlifa.com/pp-tute-2-answers/
http://home.cc.umanitoba.ca/~krussll/phonetics/articulation/describing-consonants.html
The consonant clusters are presented here.
http://confidentvoice.com/pronouncing-consonant-clusters.html
http://www.firstschoolyears.com/literacy/word/phonics/clusters/clusters.htm
Also, I suggest you learn more about whole language and phonics. These theories are generated with the same purpose of effective language learning and teaching but there are lots of differences in methodology in practices.
http://en.wikipedia.org/wiki/Whole_language
http://www.succeedtoread.com/phonics.html
http://childparenting.about.com/od/schoollearning/a/What-Is-Whole-Language-Reading.htm
http://en.wikipedia.org/wiki/Teaching_reading:_whole_language_and_phonics
http://www.phonicsontheweb.com/theory.php
http://en.wikipedia.org/wiki/Phonics
http://www.oknation.net/blog/print.php?id=459300
http://www.bkkschool.net/Clip-%E0%B9%81%E0%B8%99%E0%B8%A7%E0%B8%81%E0%B8%B2%E0%B8%A3%E0%B8%AA%E0%B8%AD%E0%B8%99%E0%B9%80%E0%B8%94%E0%B9%87%E0%B8%81%E0%B8%9B%E0%B8%90%E0%B8%A1%E0%B8%A7%E0%B8%B1%E0%B8%A2/1549-%E0%B8%81%E0%B8%B2%E0%B8%A3%E0%B8%AA%E0%B8%AD%E0%B8%99%E0%B9%81%E0%B8%9A%E0%B8%9A%E0%B8%A0%E0%B8%B2%E0%B8%A9%E0%B8%B2%E0%B8%98%E0%B8%A3%E0%B8%A3%E0%B8%A1%E0%B8%8A%E0%B8%B2%E0%B8%95%E0%B8%B4(Whole-Language).html
How to pronounce -ed and -s sounds
http://www.youtube.com/watch?v=1e_O8Gu5ICo
http://www.youtube.com/watch?v=cWjcR96r0ZU&feature=related
http://www.englishclub.com/pronunciation/-ed.htm
http://www.navy.mi.th/dockyard/knowledge/knowledge01.htm
http://evaeaston.com/t-d-Id-irreg-pattern.html
Some useful podcasted lectures from DPU are here and I suggect you follow the link.
http://www.dpu.ac.th/dpuic/page.php?id=221
