many yrs back, when i 1st discovered my interest in thai culture n travels, i relied heavily in referencing w thai peers, as well as the very trustworthy
Lonely Planet Thai Phrasebook... its very handy for phonetic reference to get pronunciation in proper order. n if sharp enough, it's pretty easy to catch the concept of grammar structure. asian languages by far apply similar grammatical rules for sentence structure.
some time later, as i grow out of the infancy language level, i referred to the
Thai/English English/Thai Dictionary to better my vocab (though the phonetics arent spelt the same as the lonely planet version)
yrs later, as i progressed from basics (becoming less alien to reading/writing thai) i now refer to varied sources of thai-english dictionaries for more vocab that comes in very handy for day to day usage in the pragmatic realms of livelihood in the land of smiles. i dun mean to boast, but i've been often mistaken to be a local.
(all of which not sparing the aid of thai peers correcting the nitty gritty mistakes for fine tuning)
bottomline, fruits will bear when effort is invested.