The most important fact about your accent in Thai is a puff of air. English adds one to every p, t and k at the start of a word, and Thai uses that puff to tell words apart. ป ต ก have none. พ ท ค have it. Say ป with your English p and you have said a different word.
You already make the sound you need, just not at the start of a word. The p in 'spin', the t in 'stop' and the k in 'sky' carry no puff. That is Thai ป ต ก. Hold a sheet of paper in front of your lips: for ป it should not move.
- ปาpaː
to throw
the p of 'spin'
- พาpʰaː
to lead someone
the p of 'pin', which you already have
- ตำtam
to pound
the t of 'stop'
- ทำtʰam
to do
the t of 'top'
Vowels that must not glide
English long e and o are really two sounds: 'day' ends in a y, 'go' ends in a w. Thai เ and โ hold one position from start to finish. Say 'day' and stop before the y, say 'go' and stop before the w.
Vowel length changes the word in Thai, and English has nothing like it. English also shortens and blurs every unstressed syllable, which erases both length and tone. In Thai every syllable keeps its full length and its tone, stressed or not.
ง at the start of a word
English only allows ng at the end of a syllable. Say 'sing-a', then drop the 'si', and what is left starts with ง. It takes a day of feeling silly and then it is yours.
Your sentence melody
English uses pitch for stress and for questions. Thai has already spent pitch on the words themselves, so a rising question or an emphatic stress overwrites a tone. The next article, on questions, shows where this bites first.